I have a feeling that Meta has some kind of internal system for slurping up everyone's contact info, and that some kind of bugs/criteria occasionally cross some streams.
Meta recruiting somehow got a hold of my name@amazon.com employer email -- which I have never posted publicly -- and started sending me recruitment emails to my work email. This struck me as incredibly unprofessional, though I understand it's almost certainly an automated system doing it.
I still don't know how they got the email address (though I guess it's just lastname+first initial, so they could have guessed?). I may have DM'd it to someone in a FB messenger chat? Maybe I used it in an "work email" field during sign up for some industry conference whose data later got hacked? A colleague accidentally merged their work/personal contact list and uploaded it somewhere? Who knows.