Still provides a good faith reason why an Amazon employee might see this and think "I need to apply the company policy on PII here" rather than a nefarious "you are making us look bad"

I think that's obviously what is going on. This is a boots-on-the-ground employee tasked mostly with responding with pre-determined answers to people angry about their orders. Of which, a number undoubtably treat their posts like PMs. This isn't someone who is tasked with any sort of decision making regarding data privacy.

And when combined with other information, constitute personal information.

address + person + timestamp = location history

Individual items purchased are PII. Timestamped records of presence at any given store might be. Store addresses, however, are not.