FB absolutely can and does correlate events and various metadata sent by the "Facebook SDK" spyware which litters most mainstream apps. ATT does not prevent that because the fingerprint it collects, combined with your IP address is sufficient to link all the separate instances of the SDK by correlating enough events.

To be clear, I'm not disagreeing with that. I'm just saying that individual applications can track those metrics for their own properties.

And, to be fair, while I don't want Apple tracking that data (however useful/useless it may be), I wouldn't want Facebook tracking it either.