I have no idea how facebook did it, but it recently asked me to add my surgeon as a friend (I recently underwent some surgery). -I don't have facebook installe

I have no idea how facebook did it, but it recently asked me to add my surgeon as a friend (I recently underwent some surgery). -I don't have facebook installed on my phone, I only sometimes use the website. -my facebook mail account is not my main one. So I am not sure how they tracked that we know each other but that's creepy as hell.