Walmart REALLY listens. I bought a few groceries IN STORE and about two weeks later I got an email with a list of items I purchased and links to review them. Now, I know what you're thinking, but I'm not enrolled in their loyalty program, and I don't have their app installed on my phone. The only way I can figure they linked my purchase to my email address is because I have previously logged into their website on my phone (via the browser) and of course my phone was with me during my shopping trip. That's some creepy shit.
Yeah, that would be much more plausible. As dystopian as Walmart is, I don't think they have phone sensors that can determine your device by just being in the store...
This is definitely how they do it, as someone who has a Walmart account and usually buys through the app. If I buy something in store with one of my linked cards, it stores the receipt in my account (and then asks me to review it)