Around the year of 2010 a friend of mine called me asking if I would be interested in house sitting, and watching his two cats as well, for about a month as he was going into the hospital for medical treatments. I accepted immediately. When I first entered his place I felt a heaviness but kept that silent. He gave me a tour of the place. I refused the basement and his bedroom. Both had a horrible sense to me.
After he left I proceeded to work on a list of things I wanted to help him out with in his home. Later on I worked on settling a bit in the spare room he had for me to stay in. One day as I was organizing some of my things in the spare room both the cats came bolting in by me and hid under the bed. I knew they got wound up but that was fear. So I looked up towards the living room where they had ran from and there walking across the floor in the sun's rays from the window, was a pair of man's legs. Just the legs. They had mechanics pants on, plus old boots. They walked slowly towards the front door. I didn't leave the room for a while. Now I'm not afraid of Ghosts/Spirits but this one had a very uneasy feel to him. I'm guessing this may be what I sensed from the start.
After my friend returned from the hospital we sat and chatted about what happened. Which brought up the basement and his bedroom. He himself was very hesitant to go into the basement. As for his room, he indicated that when he moved in there were strange writings all over his walls. Which he painted over. I sure wish he'd taken pictures.
My feeling though about this, is that the manifestation was more deliberate. By that I mean, just as ghosts sometimes cannot fully manifest due to a lack of energy, they can also choose to appear in a way they want to. The ghost that haunted my family home, could be seen quite clearly, people who saw her could describe the color and style of her dress, and the pin she wore, narrowing down a time period, but no one could see her face, even in the light of day. There was just a dark spot where her face should be. One of the psychics who investigated, told me she did not want her face to be seen, and that's why she appeared that way. If that's true, it would be just like when a robber shows up at a bank or house wearing a ski mask. It's as simple as they don't want to be identified. In my family's case, we never did find out who she was, record searches indicated the house had been rented out several times, but most of the women researched as having lived there, all moved out and lived on, dying in other places mostly of natural causes.
From your story, especially the uneasy feelings in areas of the house, the cats reactions and even the mysterious writings your friend discovered, sort of point to a ghost/spirit with a darker intent than merely wanting attention. I believe he/it appeared to you purposely as just a pair of legs, not because it didn't have enough energy to manifest, but so you not only wouldn't be able to identify him and also to elicit the very response you had, that ill at ease feeling. Some ghosts seem to purposely try to scare people, they seem to live off that fear, and it actually seems to fuel them, giving them more energy to manifest a haunting. There are many stories on this site that seem to support this.
By all means research should be done, but you may not find out much as this entity doesn't seem to want to be discovered. Depending on the circumstances of how it came to be there, that information may not be that visible. Some owners try to cover things up if it's not to their benefit. Not necessarily your friend but prior tenants/owners. I hope you can find something that would reveal some information behind your experience.
The only other thing I can offer about this, and I'm not sure if you will find it helpful, is that in my family's haunting, psychics believed that she went insane, and harmed her family. The research didn't turn up anything having taken place there, but it was curious we found it had only a few owners, a few wealthy men who owned this house in a small town. If indeed he rented to a family and someone went crazy and there was murder and insanity involved, it could have been quite the scandal and easily covered up in that era. Something like that could hurt a man's reputation as well as hurt any future profit he could make from his investment. Since my family owned it from the mid 1940's onto almost the turn of the last century, whatever happened took place in a time where that sort of thing would be easy to cover up. Now I can't prove it, despite all the investigating I did and the people I involved. I bring it up because it seems relevant, something about your story reminds me of it all and is tickling the back of my mind. Perhaps whoever it is you saw, maybe they went crazy in that house, the writings on the wall, the fact your friend said they made no sense, could be the ravings of a lunatic. Whether he hurt someone else or killed himself, I don't know, or what else he may have been involved in. Depending on the time period it happened in, it could have been embarrassing and something that could have been hidden away in history. Nowadays that stuff is too hard to cover up, but in earlier times, way too easy, especially in small towns and rural areas.
Anyways I've rambled on long enough, I'm not sure if it helps at all, I sort of follow my intuition on these things, but it does make me think. Good Luck!