Poltergeists Or Something Else?

While I have not had any paranormal experiences in the past few decades, my significant other "Derrick" has some strange occurrences in his apartment. He has lived in his apartment for at least 5 years, after his grandparents have moved out. The apartment is nice, well-furnished, and has been around since the 60's/70's.

I have hung out with Derrick in his apartment, and have not felt anything unusual. Once when we were having dinner, he referred to the "ghosts in his attic". He said that so matter-of-fact that I thought he was only joking around. It wasn't until one night that I had spent the night at his apartment.

I was watching TV around midnight and my boyfriend went outside to have a smoke (I don't smoke and can't stand the smell). His dog was sitting on my lap and we were just chilling out. I suddenly heard the sounds of someone walking around in the kitchen area. It had not been five minutes since Derrick had gone outside, and I was surprised that he came back in the house so quickly. I called his name and there was no response. Bear in mind, there is a wall that separates the living area from the kitchen, so I could not see who was in the kitchen at the time. Then, I had a strange sensation that someone was literally standing across from me and staring at me. Whatever this was, it got the dog's attention, and the dog sat up straight growling. At that point I was literally petrified, and could not move. At that point two minutes had passed, and my boyfriend had just come back inside from smoking.

I told him what just took place, and he assured me that he was not in the kitchen or his apartment five minutes ago. He then told me that his apartment was in fact haunted. He told me the most he heard/ experienced was loud footsteps in his attic. His grandparents had some experiences when they lived there, such as random objects disappearing and then reappearing. But as far as Derrick knew, no one that lived in his apartment before him had died there.

A few weeks later, Derrick had come back to his place from a late shift at work. We had been texting back and forth all day. I sent him one last text around 11:30 pm and had collapsed to sleep. The next morning I had a text from Derrick saying that "I don't know what you're talking about". I went to check my sent messages and found one that was complete nonsense. There was a string of made-up words such as "slhick mmmm up to". That was in my sent file, but I honestly have no recollection of sending that. At that point Derrick told me he had been up the whole night due to the ghosts. He complained that something or someone kept shaking him awake and had literally LIFTED him out of his bed and threw him on the floor. He didn't seem scared at all, but I sure was.

Derrick still lives in his apartment and has these experiences. I don't know what to think at this point. Has anyone ever experienced anything like this? This is really freaky...