He was talking with somebody else while his eyes were on me?

I noticed him talking with someone, and he was slowly walking away to leave their conversation. He looks back and notices me approaching his way, and he immediately turns around making his body facing me and continues to have his conversation with that person but his eyes were on me. He was laughing, smiling and his eyes were on me. I wasn’t even apart of their conversation, I was just walking past. Why would he leave their conversation, then when he sees me, turns his body to face me and stares at me with a brighten face and continues the conversation with the person. I don’t know if I’m making any sense but why would he act like that?

He was talking with somebody else while his eyes were on me?
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