Help me understand a sentence about one particular episode of History quoted from a Conan Doyle Essay

I cannot pinpoint a precise meaning of the term "policy of Tibet", but the general state of affairs might be enough to explain its use.

At the end of the 19th century, Great Britain fought over influence in central Asia, a situation often referred to as the Great Game. As the Russians were the first to make successfull contact with the Dalai Lama, the British reacted by advancing their sphere of influence in the north east of India. Advancing into Sikkim, that brought them into direct conflict with Tibet and its nominal sovereign, China.

A convention between British India and China from 1890 tried to define a border between Sikkim and Tibet and some points where British traders were allowed to interact with Tibetans. But the Tibetans considered that treaty void, as they had not been involved in its negotiation. They tried to keep Sikkim as part of their domain and to enforce their rules on foreigners. Already in 1888 British and Tibetan forces had clashed, and in 1903 a British expedition invaded Tibet. As Doyle's text is from 1902, it is not neccessary to consider further developments here.

It was an extremely sour point to the British that Tibet so harshly restricted trade contact and travel in its territory and what it considered its sphere of influence. Francis Younghusband, the leader of the 1903 expedition, published a book about his mission in 1910. There, he describes the complaints of the tea traders in the 1890s:

This Convention proved in practice to be of not the slightest use, for the Tibetans never recognized it, and the Chinese were totally unable to impress them. But it was at least a start towards effecting our ultimate object of regularizing our intercourse with Tibet, and for another three years we solemnly occupied ourselves in discussing the three reserved points...

Our principal aim was to get some mart recognized, to which our merchants could resort and there meet Tibetan merchants. We did not attempt to gain permission for our traders to travel all over Tibet, as Tibetan traders can travel all over India. We merely sought to have one single place recognized where Indian and Tibetan traders could meet to do business with each other...

Having made this concession, and having refrained from pressing for permission to allow British subjects to travel beyond this or to buy land and build houses there, we had hoped that the Chinese would meet our wishes in regard to the admission of tea... Tea is just the kind of light, portable commodity most suited for transit across mountains, and it was perfectly natural, reasonable, and right that the Bengal Government should press for its admission to Tibet, that the Tibetans might at least have the chance of buying it or not, as they pleased. But the Chinese, in spite of concessions in other matters by the Government of India, remained obstinate, and still remain obstinate...

The parallel I see to South Africa is the way the Boer treated settlers from the British Cape Colony in the Republic of Transvaal and the Orange Free State as "unwelcome foreigners". The difference, as Doyle points out, is that the conflict is not about selling tea, but digging for gold.

As a footnote, prior to the 1890 convention between China and Great Britain, Tibet is spelled "Thibet" in British legal material, at least as cited by the Tibet Justice Center: in the 1876 Chefoo convention and the 1886 Convention Relating to Burmah and Thibet. This reference made in the Hansard House of Commons protocols seems to confirm that spelling, too.

To understand the quote, and phrasing, let us first present the context of Doyle's argument (with my emphasis of the quote in context for convenience):

That is a fair statement of the Boer position, and at first sight an impartial man might say that there was a good deal to say for it; but a closer examination would show that, though it might be tenable in theory, it is unjust and impossible in practice.

In the present crowded state of the world a policy of Thibet may be carried out in some obscure corner, but it cannot be done in a great tract of country which lies right across the main line of industrial progress. The position is too absolutely artificial. A handful of people by the right of conquest take possession of an enormous country over which they are dotted at such intervals that it is their boast that one farmhouse cannot see the smoke of another, and yet, though their numbers are so disproportionate to the area which they cover, they refuse to admit any other people upon equal terms, but claim to be a privileged class who shall dominate the new-comers completely. They are outnumbered in their own land by immigrants who are far more highly educated and progressive, and yet they hold them down in a way which exists nowhere else upon earth. What is their right? The right of conquest. Then the same right may be justly invoked to reverse so intolerable a situation. This they would themselves acknowledge. 'Come on and fight! Come on!' cried a member of the Volksraad when the franchise petition of the Uitlanders was presented.

Here Doyle is comparing the announced policy of the Boer inhabitants of South Africa to that of the Tibetans, by way of arguing that while the Tibetan policy may be reasonable in Tibet, isolated as it is, it was an entirely unreasonable policy to hold while occupying the entire length and breadth of South Africa with a miniscule Boer population.

To my mind, the choice by Doyle of an obsolete phrasing and spelling for Tibet is deliberately made to emphasis the antiquatedness of the Boer position. In other words, it's one thing to be Tibet in Tibet (and even that failed a half century later for the Tibetans); but it's another entirely to try and be Tibet in South Africa.

Here, for example, are Google Earth images at constant scale of South Africa and Western Europe, side by side: