This was the first time I was in close proximity to this guy, I didn't look at him the whole time but I could see from the corner of my eyes that as he was passing by that he was glancing at me back and forth before completely staring at me without looking away. Why did he do that?
He thinks you're pretty and he likes looking at you. Don't put too much stock in his facial expression while he's looking at you. Some guys' relaxed face looks angry or weird. His face is probably just relaxed. He's probably looking at you because he thinks you're pretty and enjoys looking at you but he believes he has absolutely no chance with you. So, he's not smiling or flirting or anything because he believes he has no chance. So, he's just taking in the eye candy. I'm sure he means you no disrespect.
The chance that he's a crazy stalker or something is very slim.
If you look then it is a sign you're not a lesbian so if you looked then he might try to look at your eyes I suppose. If you just simply stop and look calmly and collectively at him and see if he has the nerve to do anything similar back then that is an attraction on a physical level. You'd be able to say hello but it is really the mans job to say hello first. He's the man. If he doesn't then he is a shy man or he didn't like your eyes. Maybe he is on drugs or is loaded.