Americans say so much stupid shit, this wouldn't warrant puzzlement, much less anger from me.

More of a "huh, that's a new one" kind of reaction.

I mean I’d say any I’ve met would be puzzled if not angry if you told them they’re not white. Probably 100% would be confused about what they are then.

So would people from north india. Are they considered white?

The stem of all this crap is that people are trying to group themselves into in-out groups based on elitism, and wanting to make themselves seem better. This is a racist and fruitless endevour, since not only are you an asshole for trying to make yourself seem better than other "races", you're also trying to diminish the cachet of other groups.

Slavs have usually been denied access to this grouping, alongside Mediterranean.

It would probably be “desirable” in the sense that it’s mostly the grouping they feel they belong to.

So do Argentinians, and the aforementioned North Indians.

To be clear: I don't think white people are superior, nor do I give a shit where slavs or other people groups fit into it. What I do think, is that it's a misguided pathetic attempt to make yourself look better if you're getting into arguments why your people group deserve to be called white.