Long, Lingering Handshake?

Guys, is there usually a reason why you might hold someone's hand after a handshake for a long time? Especially when it is your first time meeting her?

I was introduced to this guy yesterday by a mutual female friend. When we shook hands he kept hold of me the whole time our friend was speaking. He lasted nearly 20 seconds or so. It was bizarre and never happened to me before, so I was wondering if it meant something.
Long, Lingering Handshake?
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