Guy's Behavior

Does he like me? Is he flirting or bullying?

So, I just started working in a new company and everyone is so friendly and cooperative. I am actually someone who is always well groomed and professional in my work place. For this reason most of the time I got so many compliments from my colleagues. But recently I have discovered something. There is a group of (2/3) people in my office always smiling at me when I am not seeing. Like, there is a guy in that group who is very nice to me, always saying hi to me, teasing me bla bla but what have also noticed is he and team member also smile at my back, I mean when I am not seeing. And that girl was shouting like ‘Hey Man! Why are you smiling? ‘ and then both are smiling. Why they are doing this? Does he like me or something? Are they trying to bully me or they find me different or weird?
I am really confused but that guy is really friendly to me but still he and his team member is doing that thing.

what you think? Please help

Does he like me? Is he flirting or bullying?
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