Why is ‘race’ relevant here?

Because it's extremely relevant in American culture. Every culture really, we're just somewhat ahead on not lying to ourselves about it.

What the fuck is wrong with Americans and how did they become so astonishingly self flagellating.

Nothing and we're not, you're an irate ignoramus with a chip on your shoulder having an imaginary dick measuring contest because you're super duper sensitive about race.

Just on the insecure posture of this tweet, I’m prepared to bet cold hard cash that he asked her for clarity or something with a informational challenge “but does x not come from y?” Or whatever and she manufactured his reasoning and the rest to feel good. She doesn’t seem to know what et al means either.

He was literally telling her to go read her own work. The "et al" part is very fucking clearly taking the piss, do they not have humor over there in Stuckupistan? Or are your panties always in too much of a twist about basic ass descriptors to have any kind of humor about literally anything?

E: guy's post history is chock full of dogshit-tier takes with a thin veneer of leftism and a big heap of good ol' fashioned xenophobia.

They're mentioning the race and gender basically to say "a privileged person". Having privileges obviously influences your character. And race+gender correlate with privileges.

So, while there's no direct causation, and us white males who aren't chumps don't need to be offended, it's often good enough of an explanation why a particular white male might be a chump.

I agree that the usage of "white" is irrelevant here. That being said, are you in academics? It is not an unusual situation for people to not be aware of the "face behind the maths" so to speak. Granted, this is not entirely unique to women in science but it is exhaustingly common for women to be questioned more than their peers.

I think questioning this is fine as many people lie but I wouldn't take this to mean this type of situation didn't happen/couldn't happen.

This is top some top tier mansplaining here. I detect no sense of irony. Chef’s kiss.

While I perfectly agree with your position on that the "privilege" talk has become a weapon in and of itself, and that a lot of bullshit stories come out of it, I'd love it if you could change the tone of conversation.

Americans are different, and they may have cultural reasons to behaving this way. That's not to say they're right - but seeding anger this way is not gonna magically change their minds.