At first I thought it was a crazy coincidence that one of my friends' facebook profile page would appear topmost at the google search results when I was searching for... pizza via private browsing (don't ask why 😛 ). And that got me wondering - how popular can this person be? What are the odds that this person is related to my Pizza query? So I checked the same query on other devices, browsers and I even had friends run the query (while we were waiting for the pizza) on their phones and indeed I was the only one seeing this results, and only the browser sessions that where logged onto google services would I get this particular mix of results. The rest would simply display Pizza related results.
Now I can recall seeing on one of "my" devices and under this particular friend's profile a message similar to "you are seeing this result because you have visited this page on XX/XX/2018" but I can't seem to find this disclaimer anymore - I even checked if this personalization was perhaps related to my public IP or location services, or perhaps something identifiable in my router, but those other people on my WiFi network would get vanilla Pizza results not to mention that Safari on the very computer, that isn't logged-onto any google services would also get plain pizza related results.
I even checked for extensions on Opera that might be leaking (not that private mode allows extensions but anyway) but I don't have any installed!