> 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. Unity is liable for the things that they say in a public capacity.

Most contracts I've seen have clauses that specifically say that you are agreeing that the contract is limited to the terms in the contract itself and waiving everything else so you are probably out of luck there.

It’s known as promissory estoppel. The main reason promises are often not binding is that you can’t prove the other party said it. If you can prove the other party said it, and you “reasonably” relied on their statements, and suffered damages because their statements were false, you can recover those damages from them.

(IANAL)