My account was dead for about two years or so before that. Within a minute or two of signing up with my (real) email and phone number, basically my whole friend list from back when I had an account, people I've texted on whatsapp once years ago, etc. were in friend suggestions. Downright creepy.
I finally made one and I had neatly sorted real life friends as part of my friends suggestion.
That's when I realized they already had a shadow profile of me from everyone else, all I did was activate it and increase their confidence level from 95% or something to 100%...
Before Facebook, if you tried to explain to a layman that your social data can be used to manipulate entire elections, people probably would have looked at you with strange and furrowed brows. Now, it's a question of the best way to address the issue.
What usually happens is that those people have you on their contact lists, which they uploaded to Facebook to find more friends.