Two men on a sidewalk right next to me have said "oh my god, he's right there".

I work on a campus of about 5 different buildings that are separated only by a sidewalk. I was walking to the main building, and there are two men about 5 feet away from me, walking in the same direction. They were talking to each other and I couldn't really hear them. I heard one of them say "oh my god, he's right there" and I look at them and they look at me like I just appeared or something. I started walking faster because I felt uncomfortable and I heard one of them say "no no, we have to go talk to him". I started walking faster and faster and got into the building and took an elevator. I've never experienced anything like that. What did they mean? What were they talking about? If I was a ghost or something then wouldn't I have gone through them or the wall or something? I'm confused.<br><br>Edit: I'm getting a lot of comments talking about drugs. These two men were wearing a suit and tie and carrying a briefcase. They didn't sound like druggies.