I personally think the sex-workers (both trans and cis) are often sexy as hell. Hence the title.
Trans culture is more accepted in Thailand which is why their red-light district is known to have more trans people. The meme is about the awareness of this fact from western tourists visiting the area. The meme implies he has a preference but it doesn't say in which direction. Not everything that mentions queer culture is mean-spirited Lileath.
I don't think it needs to be mean spirited to be transphobic. The implication seems to be that he is tying to determine whether a sex worker is trans by asking if they are a boy. There's probably a better way to word that question, but then it wouldn't fit the meme.