Why is he scared of me?

There's this guy at work who I'm still trying to figure out. He is very outgoing with everyone. I am a reserved person and so I tend to be extremely shy and quiet at work. As from last week I noticed that whenever I am near this guy for some reason (regarding work and not talking to him), some of the other colleagues call his name and gesture like "she's there"... then he looks at me, mutters something and stop talking.

There was an other instance last week as well where he was working alone and when he noticed me, he became nervous and looked scared. He then walked away.

Just to be clear I don't think that I'm that scary as there are other colleagues in the same section and they aren't afraid of me. He's the only one that looks scared and I don't want him to be scared. Why is he acting like this?

Why is he scared of me?
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