Yea I can see how you could know. The problem is.. a tool like this has the awesome and can say "oh yes I checked all those this random APK is
definitely the one you wanted"
Thats what F-Droid and Google store (and the apple store) do: they stand their assets as "if we lied, you know where to find us" regarding the provenance of what they pass. They do of course, also routinely (ok not Apple mostly) pass apps which do heinous bad things, because it turns out there's only so much automated tests can find.
As you observe, sometimes the promise is hollow. (F-Droid)