Did they confuse assumed gender associations with sexuality?
I mean, there is a lot of social construct in gender norms, but that's got nothing to do with who you find sexually or romantically appealing.
Unless they are honestly suggesting that people who defy gender norms are now automatically considered a different gender, therefore whoever is attracted to them is now- oh you know what? No.
I feel stupid going down that train graveyard of a thought process.
By the way, even if sexuality could possibly be considered fluid in some situations, it shouldn't matter to anyone but the person or people who are actually involved.
As for the appeal to biology, not everyone has the ability or will to reproduce, and this includes plenty of people in heterosexual relationships.
The fact that there are people who are non-hetero suggests that it is natural.
They're not doing that to spite you. Seriously, what kind of weirdo would go to that special sort of effort?
Never mind that it's not your business, but whatever.