If you let other people see that you viewed their profile then LinkedIn will let you see who viewed your profile.
So yeah your theory seems most likely unless OP had Private Mode turned on for his profile (then they wouldn't be able to see that he saw their profile regardless of whether or not they have LinkedIn Pro).
Shortly after putting in for it, my linkedin reported I had a visit from a "Law Enforcement professional from the Washington-Baltimore area", which I thought was amusing.
And they'll be arrested?
Maybe you can prove them in person it is not your account, but that mean you would have to get a real visa not an ESTA.
Not if the viewer has Private Mode on. Having Private Mode off for yourself is not sufficient to see who viewed your profile.
This Linux journal article talks about how we are losing our freedom of expression and one of these areas are the war on hyperlinks: https://www.linuxjournal.com/content/whats-our-next-fight
Support social networking sites that don't try to lock you into there ecosystem by making communication less free.