Why is my brother’s coworker asking about me and staring and smiling at me?

The other day, my bro told me that of his co workers said he missed me and asked where I have been? I think it is genuine interaction. Today I showed up and he would not stop looking at me and smiling? What is the verdict on this and I think his group of friends knows too?
Why is my brother’s coworker asking about me and staring and smiling at me?
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