> he has every right to ask for it

Who says so?

If it's not in legal text, it doesn't exist, or matters.

If you don't want to support it, make it clear in license or README. Lots of projects work like that. Companies put "source available" or "open source but no external contribution" projects on GitHub and make it very clear what's the expectation. Nobody has any issue about that.

Somehow this guy thinks he is special.

If someone doesn't understand how licenses work, they should keep their work close sourced.