The article says he did not want to criticize "Google or other companies" until he quit. That does not imply that he quit so he could critize Google specifically. It seems pretty simple: a senior employee of a company typically doesn't critize the employer; and, a Googler doing AI criticizing other companies (such as OpenAI) would undermine his message. So he quit so he could freely criticize everyone in AI.
Another example of them doing this was with the "freedom" protestors in Canada. They claimed that a majority of funding for these protestors came from Canada. While yes, technically that is true, the full context is that some >40% of the funding came from foreign influencers, which is a figure that would alarm anyone if they actually just put the percentage right there. So they were technically correct, but still spun a narrative that was different than the reality.
Given how forcefully Hinton seems to have expressed this opinion, it would be easy for them to have included a sentence to better clarify his intent.
p.s. heck, almost every job I leave involves a bit of negotiation with benefits dangled/hostage to sign non-dispargement agreements. Do you really think G. Hinton walked away from Google without signing anything?
https://news.ycombinator.com/item?id=5365579 // grep for salary discussions
Not as much as it depends on how many millions somebody already has, no.
Again, if you're sensitive to income loss, the answer would be to not trade ethics for money in precisely the way he just did. The probability of refusing to sign speech-curtailing agreements as you are quitting your job to gain more ability to speak freely is really extremely high.
Also, you might notice that this discussion you linked to about his compensation is from ten years ago. The benefits being discussed have already been accrued, for ten years.
p.s. per your speculation, he should feel free as a bird to tweet back "heck no, that's why I quit". (Kindly report back here with the answer and let us know.)