Can Anyone Explain this hanshake?

It sounds to me that perhaps he was remembering you from the years ago, like you said. When the opposite looks into your eyes for that period of time, he WAS being curious, just not the type of curious you may have thought. Just put yourself in his shoes, him being a male, most likely a flirt, and he was just doing a tad flirting. Overall, though, he just wanted to remember precisely who you were. Hope this helped.^.^