It's just that the word is racist, not homophobic in this case. (A racist person, for example, will hate black gay people even if they aren't homophobic, and that ofc doesn't make them any better of a person. Any prejudice would be against monosexuality, not homosexuality. Nothing about this post, even if it intended to call monosexuals cavemen, would be homophobic. It clearly supports homosexuality in bi people, as well as treating homo and heterosexuality the same.
Homophobia is a prejudice against same gendered attraction or people who experience it.
That was more of a sidenote, but to clarify, I was saying that homophobic isnt even the right word.