Ouch. 😬I created a blank test account linked to a burner email. Right out of the gates it gave me lots and lots of friend recommendations that I was connected with on my primary account.
Do you have cookies and trackers on your browser? That's the only thing I can think of.... or it is tied to your IP address and connected it to your main account. There's got to be ways Facebook can track people that we don't know about, that aren't immediately apparent. I have no doubt Facebook has certified geniuses working for them to figure out clever ways to track people.