I do not understand this argument (Side Note: I am fully supportive of the idea of being nice, encouraging, and forgiving towards people in Open Source development).

Unless The Linux Foundation (which is what pays Linus himself) states a code of conduct, and says that it will dismiss Linus unless he follows it, I don't see why he has to be respectful of, say, Intel's code of conduct. Also, what about an unpaid volunteer? Why should they respect corporate codes of conduct when they are not being paid a single cent?

Two Intel engineers working on Intel's internal kernel fork may well have to do that. But the precise reason it is an Open Source project is that it is unaffected by corporate policies of any sort. This applies to "codes of conduct" just as much as it applies to "keep your [computer] code 100% private".

It is still 'just' an OSS project.