As a counterpoint, why should a “metal finishing technique” be proprietary? Lying to the vendor that Apple said it’s ok is obviously wrong, but an employee taking that knowledge in their head doesn’t seem wrong to me. We have moved past the age of indentured apprentices and the freemasons.

Because Apple paid to produce that knowledge? It's good that people can spend a lot of time and money developing new knowledge and then for some period of time they get to exclusively reap the rewards of doing so.

Do you mind if I MITM all of your work output, your emails, your code, your messages, and attach my name to it and then receive your paychecks in exchange for my work?

To me, the fraud is the issue. If the person actually has the knowledge to spec out the whole technique, then sure, they can ask for it. But if they just said "give me what you give Apple" or describes it in detail and the vendor says "no I only will give that when Apple says they're okay", I don't see anything wrong with that either.

My reading is that the employee did not know the method but only of its existence.

It must have some sort of value if OpenAI went through the trouble to get access to it.