at this point in the story some of the humans Lilith (the protagonist) is supposed to be leading have gotten it into their heads that Lilith might be trans (not how they phrase it), & that her SO, Joseph, is gay (not the word they use). (Both Lilith and Joseph are straight & cis, as far as I know.)

This is of course a thing which happens in real life—you'd probably be able to find examples for any famous person if you trawled enough right-wing conspiracy theorist sites. Sometimes when people try to dismiss these claims, though, the way they phrase it (e.g. "I can't believe people would say that kind of thing about [person]") comes across as (implicitly) "being queer is bad", and (more explicitly) "[person] is not bad", therefore "[person] is not queer". I don't know that Octavia Butler is necessarily doing that here, but it is worth noting that so far, at least, there haven't been any queer characters.

I think there's a lot to say about this book from a queer theory perspective (I haven't even mentioned the ooloi), but while I'm not unequipped to talk about that, I'm certainly not the best person either.