That's why they removed the repo too, too easy to see the changes.
Also I’m not sure how are “promises” legally binding unless they are part of a contract?
You'd be surprised. Claims that are made as part of any marketing material or promotion can absolutely result in lawsuits if someone built their business on that claim and then Unity screwed them over. In that way at least, Unity is liable for the things that they say in a public capacity.
(IANAL)
This doesn't follow - it's entirely possible that the execs planned to do this, a bunch of dev's said "that's insane and we'll quit if you do this", the execs followed through, and the devs followed through on their threats to quit.
They would have to be, because deniability is important for a gambit like this. I'm not sure how you would announce "we're going to psychologically manipulate our customers" to the team anyway.