Guy gives me serious looks and stops what he is doing to look at me. What does that mean?

I rarely interact with him because we work in different areas and our paths do not cross.
For instance, one time, my colleague, I and her niece had to take something from the place he was working with. We took the thing, and while talking to my colleague, I asked her what time was it, and she said ”11.50”. I replied to her enthusiastically ”10 more minutes to lunch!” and he said, concentrated on the game he and his work colleagues were playing, ”I know that after 10 minutes it is lunchtime”. I ignored him.
A few weeks later, my mother and I prepared to leave the workplace, and he was passing by the roadside with his colleague. We stopped at the last stair due to the fact that my mother checked for something in her handbag, and I glanced at the trees. Then our paths crossed, his friend looked at the road while he was staring & vice versa at me/him for a few seconds (3 seconds, it happened quick). Then I broke the eye contact because my mother asked me something.
Approximately a week later, I was minding my own business waiting for my other colleague to go feed the peacocks, and he was around my area going to the vet and back again. He passed next to me and as he wanted to close the door, he looked at me and after I said ”Good afternoon!”. The guy didn't respond, just had this look with a tent of shock (?) and we made eye contact for a few seconds, then my colleague came and I turned to look at him. After we left, he closed the door and left.
Some time later, I was sitting next to the same colleague who was in the previous situation, and he was talking about something (cannot remember exactly what) and I went to pick up something (I told the colleague that I am listening to him, just going to pick something), because I was sitting on the stairs while the colleague was standing up. When I picked it up, I looked up and he was staring at me, the same facial expressions like before. We held eye contact and I went back to my colleague to continue the conversation.
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P. S. — His friend asked me to go camping with him, the guy and plus a couple of his friends. I'm thinking of bringing my best friend.
Guy gives me serious looks and stops what he is doing to look at me. What does that mean?
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