Unknown device under protocols

Under "Logs" I find the entries for a device that does not belong to me and is not under my control. I assume that happens because its owner registered it with the wrong ID.

I find this disturbing, especially because it does not correspond to my understanding of privacy protection if I can meticulously track the web history of a person unknown to me. So, I've tried to alert the person by blocking a few of the addresses he or she is accessing (but I do not).

That hasn't helped so far. Is there another method? I tried setting up an appropriate redirect, but that didn't work due to https certificate issues. A viable option would be a block page with an individual message.