I think the memo made two mistakes here.
The first, from my perspective, is that it crossed a line that you really have to tread with care when it started talking about "biological IQ". Anyone familiar with the sordid history of eugenics knows that you tread that line really carefully, both because of the sordid history of policy on that sort of thing, the extreme difficulty of separating biological vs. environmental constructs for IQ, and the difficulty of creating a single "IQ test" that measures every single aspect of human intelligence. The quote about "IQ and sex differences" (being something the left ignored) was only supported by a link to conservative think tank Manhattan Institute for Policy Research (which said some things about bias in science grants, but didn't really have anything to say about IQ and sex differences).
This is the point where, to me, the memo went downhill. I am not sure it is the intention (possibly the emphasis was intended to be more the politic), but it is very easy to infer inferior / superior claims at this point, because the whole "IQ and sex differences" thing sort of came out of nowhere.
The other reason it went downhill fast, and unnecessarily so, was because the paper brought in "liberal" vs "conservative" American political dynamics elements. BIG mistake. Any discussion along this line needs to be as apolitical as possible, lest it descend rapidly into toxic left-wing vs. right-wing tribalism territory (as, well, happened). Instead of attempting to skirt around politics, loaded phrases were used, particularly at the end of the memo, like "PC authoritarian", and sourced links typically were op-ed, often with strong bias.
I agree that a lot of the memo is more some of the tribal / "role" paradigms and elements that have been discussed in many sources over time, and there's actually some interesting food for thought in it. I'm not terribly comfortable that what I see as poor communication skills led to the firing. I would not characterize this memo as "polite" though, for the above reasons.