More often then not I've seen where people who are trans are still attracted to the gender they were attracted to before, there are exceptions but most of the time that's how it goes.
How is that homophobic? Yes I obviously don't know them or their sexuality, and the comment wasn't supposed to be taken seriously, just to state how good dick feels in a vagina.
I think I read it as much more serious than it was intending to be, to me it seemed like the person was denying the idea of them being homosexual because they are conventionally "straight" now.