Non-scratch org list shows a (U) on the left of one of the org username.

The force:org:list command displays username for the orgs that have been authorized and the active scratch orgs that have been created. I don't have any active scratch orgs, but in the non-scratch org list, it shows a (U) letter on the left of one of the org username. According to the developer doc, U points to the default scratch org username, but I don't have one and instead it should have been (D) which points to the default dev hub org username for that org username. Why U is there for a non-scratch org? The org which has a U on the left is a developer edition org that I've authorized.

Thanks!

#Visual Studio #SFDX CLI #Scratch Orgs #Salesforce Developer