I wrote Brian Ray asking him about Paul's bass technique and he answered me back almost instantly!! If anybody knows, I imagine it would be Paul's bassist.
He says Paul ALWAYS uses a light left hand muting!
Edit: I just realized I misspelled his name. I'm glad he responded anyway!
Listening to the tracks, the palm muting has sounded quite obvious to me for some time. Glad to hear Brian cleared that up.
I think Sir Paul is probably a little reticent about letting too much out about his creative process. Some of that might be his competitive nature. But I think it can also be attributable to the fact that he may not want to overthink things too much. Hence his lack of gear knowledge, too.
!! If anybody knows, I imagine it would be Paul's bassist. 