I regularly have people show up on my "People You May Know" that have no mutual friends with me, and I don't know them so they certainly don't have my email add

I regularly have people show up on my "People You May Know" that have no mutual friends with me, and I don't know them so they certainly don't have my email address or phone number. Oftentimes it's people who went to the same university as me, so I wonder if they base it on friends of friends of friends and other less direct connections.