Does a year 1900 meeting in a Masonic Hall imply that it was a meeting of Freemasons?

No, there's no reason to infer (from the information given) that the meeting was Masonic. In fact, from the phrasing "a large an [sic] influential meeting", I would infer the opposite.

The discussion of political topics is strictly forbidden at a Masonic assembly. Thus if the meeting was about the use of public funds for creation of the Bowling Green it was a political meeting, and would absolutely not have been a tyled Masonic meeting. This principle is fundamental to Freemasonry, so that it can build a sense of community across political divides.

Alternatively, if the meeting was about a charitable endeavour by local Masonic Lodges, it would have been a joint business meeting organized by, and attended by members of, those local lodges. Even if all in attendance happened to be Masons, by virtue of being members of the local Lodges involved, this would not have been a tyled Masonic assembly. Non-Masons might have been invited to make presentations for and against the proposal. Such meetings are common when, for example, multiple Lodges jointly run the non-profit holding ownership of a shared Masonic Hall.

Finally, if the meeting was about a charitable endeavour by a single Masonic Lodge: then yes, that meeting would have been a tyled Masonic assembly (of that Lodge). However large the Lodge might be however, and some Lodges can run into hundreds of members, the meeting would neither have been well publicized nor regarded as "influential". While the minutes of each Lodge meeting do not contain any masonic secrets, and are over time released publicly for historical research, they remain the business records of the Lodge. In general, prior to becoming merely historical records, they will only be shared with auditors and with the Provincial Grand Lodge holding jurisdiction over the Lodge.

Note that while all Lodges hold non-tyled "executive meetings", under various names: all business decisions, and allocation of funds, can be authorized only in a tyled Lodge Assembly properly announced to the full Lodge membership. Any charitable endeavour so approved would then simply be announced to the recipient as granted.

The Grand Lodge of England reports that there were 2800 [or so] Lodges operating in England [presumably meaning England and Wales] in 1900. Likewise it reports that over 3000 English Masons died during the First World War, of a total of 880,000 British casualties. Estimating that to be 80% English gives about 700,000 English casualties, so Masonry represented roughly 1/2 percent of the English male population in the early 1900's - a high point for Freemasonry in both the British Isles and North America. (It might have been higher though, as the minimum age to become a Freemason is 25. If casualties skewed to men younger than that, a larger percentage of the male population older than 25 might have been Freemasons.)

Note that Freemasonry keeps detailed extensive records of all Masonic Meetings, and these archives are in general open to non-Freemasons for historical research. You could inquire further from your local Masonic Lodge(s) about records concerning involvement with the meeting in question.

Tile (1928 OED online):
2 Freemasonry. (Usually tyle.) To protect (a lodge or meeting) from interruption and intrusion, so as to keep its proceedings secret, by placing a TYLER before the door. ....

From comments above:

• Don't be misled by an impression of small Masonic Halls. Here is the Scottish Rite meeting hall in Hamilton Ontario, that has permanent seats for near 500 and can hold perhaps another 70 on the floor on temporary seats.
  

• Other rooms in that facility have been used not just for weddings, but also high school graduations and the shooting of episodes of both Bomb Girls and Murdoch Mysteries TV shows.

Right through into the 1970's it was common for Masonic Halls to be the second or third floor of a downtown commercial establishment. The last of these in the Hamilton Ontario area was the relocation of Union Lodge #7, G.R.C., from this second floor location just a few years ago: