But if you think he is male, and that it won't make any difference, why would you choose to call him 'she/her'?
I dont mean to badger, I am genuinely interested in the reasoning. Part of that is because I find I tend to defer to 'what someone wants' for the desire for a quiet life, to avoid conflict, or to avoid hurting someone's feeleings, but that's not an issue here.
So what makes it 'the right thing' to do?
I think we are socialised and habituated to going along with what people ask, especially if we are women, and that's okay for the most part, but it can have impacts.
Cumulatively, constantly acceding to the demands of others that carries over even into a space where we acknowledge it doesnt matter means we are expending mental energy to appease people at the cost of our own ability to speak freely, state our own boundaries, state the truth.
I find it interesting to what extent we are willing to follow instructions even when they are not necessary. Not directed at you or anyone in particular, just musing.