Calling a guy and he doesn't remember me?

I met a guy last Friday. The guy is a friend of my friend. Last Friday, he seemed to be into me and my guy friends thought so too. Anyway, before he left he told his friend (our mutual friend) to give me his number. I just called him today because I just received his number. When I called, he didn't seem to know who I was so I just hang up the phone. Did he forget because I spent 5 days without calling? I thought he'd remember me because we talked for a while when we met.
Calling a guy and he doesn't remember me?
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