What is the meaning of “found myself sitting in there”?

I found the following sentences on a TV series. The conversation happens when the mother of the guy was sitting on a chair in an old building. And while the mother was going somewhere, she sees the man’s car pulled over outside. After that, she stops by to ask his son what he was doing there.

Mother: I was on my way into town and I noticed your car.

Son: Yeah, I stopped by to see dad and somehow found myself sitting in there.

Though I could guess that the meaning of this phrase could be to indicate that he hadn’t had any plans to visit there and stay sitting there, I am not precisely sure about it. What’s more, when we analyse these types of phrases, we could learn more related phrases and associated grammar. That’s why I wanted to ask this question.

Therefore, I would be grateful if someone could let me know what is the exact meaning of “found myself sitting in there”.