As others have said, him recognising sex exists because it advantages him in some way doesn't make him any kind of an ally. It makes him a resource.
I've forgotten who said it recently - I think Natasha Chart - but setting aside purity politics and pragmatically treating those with whom we disagree as a resource is the clever thing to do, especially in times such as these.
If I see people that get us closer to our objectives as resources instead of allies I'll be far more likely to be able to achieve something worthwhile.
So, if a sexist dickhead inadvertently advertises the gross unfairness of identifying into women's sports, so be it.
I'll take that amplification of a message and it's benefits, whilst denouncing all his shitty views, and leave owing him nothing.