my first T told me that while she believed there was a spectrum or whatever and a lot of people were actually in the middle (a fluid sort of thing, like it is with me, really) she was most definitely on the heterosexual end. I didn't feel offended at her, because she was just being matter of fact really about how she was solid in her own sexual identity but accepting of the fluidity in mine. she was more definite in that nothing would ever happen between us because it wouldn't even be ethical - and she was ALWAYS ethical, whatever her other mistakes were!
your T might have been less tactful than she should have been or clumsy in that particular statement, but I don't think she meant any offense, rather that she just wanted to be clear about her sexual identity as well as being clear that there wouldn't be any unprofessional advances, probably.
I think you're handling this in a clearheaded, appropriate way too.