I am 99% sure LinkedIN used my IP address to match with my second floor neighbor, despite their claims that they would never use IP address as a connection data point.

I was sharing my wifi for a brief period with my neighbors on the second floor. My neighbor had a new room mate. The guy was from another country. He didn't work in the same industry I do. I didn't have any of his contact information anywhere on any of my devices, and afaik, vice versa. We had no formal contact in any fashion, monetary or electronic communication or any other kind of contact other than passing each other in the hall. I didn't even know his name. He's just one of millions of people who live in my region.

Yet they suggested him as a possible contact.

If they weren't using IP address, they were using black magic.

edit: to clarify, i forgot to mention that i had no linkedin connection to my neighbor, afaik he didn't have a linkedin account, he definitely doesn't have one currently. He was sort of a luddite, barely used his computer, and i don't believe we ever emailed each other, or even had each other's email, I just searched my mail and have record of any.

And I very much doubt my neighbor had any obviously traceable connection with the roomate anyway, at most a phone number and received rent through cash or check.