I'm a white man. I can absolutely generalize about a well known aspect of reality. It isn't in question that white men are currently in a position of overall privilege, and that as a group that position of privilege has the effect stated.

I pretty much also said that this is true in the western world where white men are the supposed majority. I said that the same would be the case with any dominant group because humans are just like that.

A generalization can not only be true in general, but it doesn't inherently mean that the entire group is at fault (beyond any unintentional benefits from the situation, which is what's called privilege in current discourse on matters of gender and race in specific, but applies to more than those alone).

Here's the thing. Until and unless we, not just as white men (speaking of the group I'm in) work on calling out and correcting bad behaviors as a group, to the point that it ceases to be a problem for others, we are part of the problem, no matter how little any individual likes that.

Divisions currently exist. They will always exist because any time there is a place of authority/power, there will be those that seek it and use it. Over time, you might see a given demographic shift in and out of that place of power, but it won't change humans being humans; there will be abuse of power.

That's the real key. The fact that white men have held dominance over most of the world for centuries (for a given value of most, and a given value of white) is simply fact. One could argue that the position of dominance really covers all the world since anyone wanting to disrupt that has to contend against that hierarchy. There are definitely places where, within a region* white men aren't the dominant group, kinda impossible to be otherwise. But trying to pretend that the world isn't the way it is is just silly.

I think the generalization isn't really about white men per se, but about the demographic in power. Give a group unchecked power long enough and they forget how that came to be. I agree that it's not a rule, and maybe should be expressed as more of a heuristic: if you are speaking to someone that is in power, and you don't look like them, they might think you are not empowered.

Don't let the lack of nuance in that statement take away from all the very valid points being made. The plight is real, and hopefully the white men who are enlightened enough to not confuse circumstance with natural order will read and know to not take it personally.

What other reason would you suggest as to why he would assume that he knows more than her or that she couldn't be the person that he's referring to? Clearly he didn't even know her name yet so what did he have to go by to draw those conclusions? It obviously wasn't her lack of knowledge on the subject that they were discussing now was it?

Gender not important also, loads of women "mansplain", it's a problem with attitude, not gender or race

Because the 'splaining phenomenon is about perceived but unearned superiority which leads the 'splainer to 'splain to someone who knows a great deal more than they do and, crucially, someone who the 'splainer ought to realise knows more than they do but doesn't because of the illusion created by the society they live in.

I'd have added "(born) middle-class" because that's an important part of it too.