Earlier quoted context omitted.
If your Amazon receipts go to Gmail, Google collects not just all of that data, but from every other site you've bought stuff from: https://www.cnbc.com/2019/05/17/google-gmail-tracks-purchase...
Google stopped mining Gmail two years ago: https://www.nytimes.com/2017/06/23/technology/gmail-ads.html Any aggregation or segmentation of emails by ML/AI algorithms, as your article talks about, is analogous to having smarter filters in your inbox. It's tech illiteracy to confuse these perception NNs with data mining for business purposes.
It is absolutely mining email, and it's extracting purchase data from it, that isn't even used in Gmail or revealed to users in any visible context, it's buried in settings. What Google uses it for? I don't know, as you said, they claimed they stopped using Gmail data for ad targeting purposes two years ago. But they're definitely working on extracting this very valuable and marketable data... for some reason.
Is it possible that Google generically collects user purchase data, including from Gmail, and then whilst not using "Gmail data" for ad targeting, it does use the "purchase data" which has been generically made part of a user's Google profile? That'd be splitting hairs real close, but it'd probably be good enough for the lawyers.