My take would be that this cis guy should also reject trans men like fellow human beings, rather than as symbols of an entire identity group! It's never a good idea to reduce someone to their identity and to say you'd never date a member of their group -- it's disgusting when guys on Grindr do that on the basis of race, body size, or disability too. A quick "sorry, I'm not interested" is really all it takes to treat someone like an individual rather than an entire category, and everybody with a health respect for consent can move on from that without issue.