I'm going to be unclear about some of this intentionally to be in line with what's been reported by Digiday, and not speculate too much based on what is likely from this.
Amazon recently upped their advertising offering for banner campaigns, and are selling customer match data to advertisers within their self-service platform.
You can target Amazon customers on and off Amazon by demographic and by importing user data through hashed email lists. This is relatively common throughout Display advertisers, but represents a big step up for Amazon to match Google and Facebook in targeting options across Display networks.
Selling this data isn't possible for a normal website.
The reason Facebook and Google did it is because you're basically permanently signed into both on mobile devices, and their apps provide sufficient information to identify *all* of your devices and join it into a single identifier.
This is known as cross-device matching. And Amazon have that capability. And Amazon are behind in the search-tech market quite a lot.
So their offering has to be better, but also probably won't beat it by tech offerings alone.