Well, that part was added later, so I didn't see it at the time I made my post.

In any case, I don't think that makes any difference. The paragraph above and the law clearly states that it's the marketing carrier that decides the baggage allowance. In this case, that'd be United. When you go to UA's own calculator, it asks for all requisite information, including origin, destination, elite/cc status, and marketing carrier. It clearly states that the first bag is free.

Secondly, that wording is not clear at all. In fact, I don't think it even refers to baggage fees.