Sometimes these negative or low emotional vibes can be misinterpreted. Sometimes not. I find that usually, it's not an evil presense, it's an emotional wreck that's actually the ghost.
I'll agree with you on that Lope, emotions can and will be misinterpreted resulting in someone drawing the conclusion that a spirit is evil when it's encountered.
However, I will say this is a first that I've ever heard of an experience where someone had simply been near a location and had been followed back home only to experience a certain amount of personal torment that others had been able to pick up on later when they visited.
UNLESS it was enough to have just been aware that the place was haunted by some negativity that had been a factor in the unintentional "invite" to follow him back home.
Whether or not UNLESS could be the case, I'm all too interested to know if anyone who worked there had an experience similar to that.
It may just be my opinion but I don't see how anything could be mistaken or misinterpreted in this instance. I won't say evil but one word that does come to mind and came to mind when I first read about this, to describe whatever it was that followed Kats home, is malicious plain and simple.