In F-Droid (not sure about Play or other app stores) K9 v8.0 (and above I guess) is now listed as Thunderbird Beta for Testers. I and possibly others thought that the K9 version of the app would keep it’s branding all the way through, including it’s listing name or title in various app stores. Perhaps it wont or perhaps it’s a listing error. We’ll see.
Apparently it’s a metadata bug, K9 shouldn’t be listed as Thunderbird. See comments ITT.