I'm really confused!?

I have this really cute neighbor (he's Russian) that lives in the floor above me. I see him about 1-2 times a week and we always p by each other in the hallway in our apt complex. One time we were walking towards each other and it was like a complete stare down. I smiled at him but he just kept staring at me with a straight face! Then when we got close to each other he said "hey" and I said "hi" back and we proceeded our way. Also, sometimes when I see him, I smile at him but he stares at me with this kinda pissy look and it made me worried! Does anyone know what this means or what kind of body language he's giving me? I feel like he thinks I'm a freak! Maybe it's a Russian thing...?