I have no idea how it repopulated your games. However, that said, I've also never heard of the store not requiring an account to be signed in order to download ANY game, so if it allowed this in your case, it may have tracked it somehow. It's just not something that's come up before and I cannot find anything on the web about a Windows 10 Local Account keeping game history in Microsoft Store.
The closest I can find that might apply here is tracking of Activity History in the Windows install which is explained here:
https://support.microsoft.com/en-us/windows/-wi...
Others may have their own ideas. There are some pretty smart people around here.