What they and other companies are doing with available publicly available data (whether copyrighted or not) is a matter of fact and subject to law. The opinion of their executives on copyright regimes is pretty much irrelevant.
Given AI is entirely dependent upon copyright theft, what he had brought to the table could have resulted in a judgement against OpenAI that they didn't have rights to use the content. For example, maybe he had proof that internal analysis concluded that what they were doing was indeed copyright violating.
If it were judged as such, the company - and indeed much of the AI industry - would be sunk overnight, as they'd be liable for violating the copyright of tens of millions of people or more.
NVIDIA is making $60BN in revenue this year. If AI training is determined to be theft and all existing datasets are determined to be poisoned, the industry falls apart instantly. All the R&D NVIDIA is pumping into maintaining its lead, all the contracts with fab houses - suddenly is a giant tank of red.
All the investors in SV who have pumped giant piles of cash into AI startups - they'd lose everything.
You think someone wouldn't be killed over that?
The AI industry has whipped itself into a trillion dollar house of cards and something like this could have been the finger flick. The US (and allies) started a war that kind of money.
[0] https://en.m.wikipedia.org/wiki/Dowling_v._United_States_(19...