Phantom device showing on Google Play
If you're sure that you never login to any Android physical devices recently, then there's a possibility that you're using Android emulator with Google Play services (e.g. BlueStacks), and login your Google account on it.

Based from observation (this question, self-testing, and another source), BlueStacks tends to emulate Samsung devices. As explained by jpr on AndroidCentral forum,


  Well, BlueStacks has to show as some type of device if you connect to Google Play to download apps, or you wouldn't be able to download apps from it. Which device it shows as can vary. It historically has been some type of Samsung device, usually a Galaxy, and usually is a T-Mobile version, but of course they could have randomized the carrier now or switched to AT&amp;T to avoid easy detection.


(minor copyedited)