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.