On iOS, certain things intentionally survive app deletion, most notably the Keychain. Credentials stored there are not removed when you delete an app, by design. I mean, it is shared with web login, and apps do have associated domains.

I'd have to check if apps can read your phone number, I think they can, that's one of the standard UUIDs for a lot of messenger apps.

And apps from the same group can have a shared set of preferences. Or could: I never needed to add that feature to any app I've worked on, so if it was ever removed (or if I misunderstood the mechanism) I never found out.

Now, back in the iOS 4 (5?) era I did manage to get the horrifying situation where a factory reset(!) device was still getting push notifications for my twitter account (with no app installed), so I won't say nonsense can't happen (and you listed Meta apps, and Meta have a reputation for pushing the limits on exactly this category of nonsense), just that what you're describing isn't a smoking gun.

Many apps look for authenticated sessions across their other apps to log you in. Google does this too.