Guys, if a guy looks at you when talking to a group or enters a room?

today a guy colleague who sometimes glances at me walked into the room and said hi everyone but the whole time he was looking right at me, into my eyes. he was still looking at me when he started to talk to another colleague and then looked away. why would he do that?
Guys, if a guy looks at you when talking to a group or enters a room?
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