score:4
It doesn't matter where your ticket will take you, as long as it will take you out of Thailand. That's why it says "onward or return" ticket.
Upvote:1
They don't know or care where you're coming from. They don't know or care where you're going.
Supposedly, they care that you do leave, but the truth is, if you are white or have a passport from a white-people country, they don't even care about that.
Once I entered Thailand by mistake. My ticket was (IIRC) to Saigon, but I thought it was two tickets, not a layover. Nobody mentioned anything, until I tried to get my boarding pass to leave, and they definitely wanted their 500-baht airport fee, in cash.
If you are from India or China or, Buddha forbid, Cambodia, then yeah, they might want to see your return ticket.