The link above, https://mail.google.com/mail/u/0/#search/category%3Apurchase... is just a search of your Gmail inbox for "category:purchases". You get exactly the same results by opening Gmail and entering "category:purchases" in the search box. Each of the results is an email that was delivered to your Gmail address, i.e. an email actually in your Gmail inbox or archive. So if you're saying you're seeing someone else's purchases, it means email meant for them was delivered to you (and you didn't notice it at the time for some reason). You can click through to each individual email to see when it was sent and by whom etc. So if it's a bug, it's a bug with Gmail delivery itself; it's not a bug with the purchase categorization specifically.