When a given demographic is a dominant presence in a given area (not necessarily work, it can be anything), there is a tendency for they demographic to start making assumptions about other demographics.

In most places, men are the dominant presence, and in most of the "western" world, they will also be white.

In this case, the individual who a white male was doing what's called colloquially, "mansplaining". He was correcting a woman when not only was the woman right, but was the very source he was using to correct her.

This is a consistent and very unpleasant fact of the world that white men will treat anyone of any other demographic as less than equals.

In this specific case, I suspect that the person making that post was pointing to the prejudice and stupidity of the person indirectly insulting her being a systemic issue arising from both gender and sexual entrenchment along with the privilege that allows the dominance of the white male demographic despite their being no quantifiable factor for that group to be dominant other than that privilege.

She, in other words, was pointing out a systemic issue by using an anecdote. Which can be a bit difficult to accept as evidence. Or would be if there wasn't a good century or so of giant piles of anecdotes from real people pointing to that systemic issue not only existing, but being something that holds everyone back.

Truth? Yes, women and people of color are going to assume they're right and whoever they're talking to is wrong just like any humans will. But white dudes have been pulling that crap for multiple generations, and anyone that isn't both white and male get sick of the bad behavior.