This is getting off-topic but it's basically two parts: the first being the he attended an optional “Diversity and Inclusion Summit” and had a strong emotional reaction, which he made an effort to circulate around the company for several months. It's loaded with emotional language (“an ideological echo chamber where some ideas are too sacred to be honestly discussed”) and claims of authoritarian oppression. That inflammatory rhetoric is what cost him his job because it clearly wasn't just a scientific discussion and left quite plausible grounds for anyone working with (or especially, had he been successful in making it into a leadership role, supervised by) to claim a hostile working environment — which is why he dropped the NLRB claim after it was looking like it'd be unfavorable[1]. Even if you think they're wrong, publicly putting your management in a position like that is unlikely to end favorably.
The second part is the painful irony of his positioning himself as a Man of Science Protecting The Enlightment Against Dogma!!! but what he wrote was a poorly-edited (and don't forget, what finally leaked was presumably better after the several rounds of editing prior to it being published) rehash of traditional reactionary arguments for biological determinism with only a few references to peer-reviewed literature, with little discussion or signs of familiarity with their fields, and instead relying mostly on links to broad Wikipedia pages and conservative blogs. Note how much work it was simply to summarize his claims clearly enough to evaluate them in https://medium.com/@tweetingmouse/the-truth-has-got-its-boot... — that's the most point-by-point examination I've seen and it's considerably longer than the original.
On its own failing to perform at the level of a good student essay would be embarrassing but given the topic and how quick he was to cast this as political oppression while taking as little responsibility as possible for his own actions, I think it warrants the use of “tantrum”.
1. https://arstechnica.com/tech-policy/2018/02/federal-labor-bo...
