The most likely explanation is that you did it and have no memory of it; this can be caused by taking certain sleep medications, having a sleep disorder, or by other environmental conditions (like a CO leak, already mentioned).
The next most likely is that a friend or family member with a bizarre sense of humor is playing a prank on you.
It is more likely that you own a cat, who is literate and can operate a computer, than that your system was remotely compromised for the purposes of renaming your bookmarks.
However, the folder in particular was a collections of links, one of which I suspected had a virus. So I named it "folder with possible virus links". I can only imagine whoever was in my computer, could not resist renaming this.
I have no medication, no negative environmental conditions and I am, by normal standards, a sane individual.
This reminds me of something similar that I experienced.
When I was younger my mother and I started noticing food missing in that there would be less of a bag of chips than we recalled. Nothing was ever completely eaten and the food had to have been opened first. We were pretty sure something weird was happening, and then one day we got home and I noticed there was a can of pop missing. I was absolutely certain I knew how many were left, so at this point we were convinced someone other than ourselves was responsible. After talking to other residents in the townhouse complex we find out we're not the only ones that this is happening to.
Fast forward a few days and I'm locked out of our townhouse. I went to my friend, who lived a few townhouses down, and asked if I could hang out for a bit as I was locked out. He proceeds to tell me that the caretaker's daughter who lives in one of the townhouses has a master key and can let me in, as she did it for him before.
We walk over to her place and he asks her to let me in with her master key. I will never forget the mix of anger and fear in her face as she weakly tries to deny having the key, only for him to bring up past incidents she has let him in. She relents and walks us over to my townhouse and lets me inside.
Amazingly, after that day we no longer had food and pop go missing.
TLDR: carbon monoxide is a helluva drug
It was a very strange feeling. Whoever had renamed it was replying to the subject of the bookmark folder. So Eg. If the folder was called "Fast cars", then it would have been relabelled something like "I, this is fast cars pal." Both the "I" at the start and the "pal" are typically Scottish, which is where I'm from.
I deleted the folder.