why he believed is the same why anyone else believes it first time. everyone supporting or simply using bitcoin went exactly through the same thing as the first guy. at some point you simply see it as a valuable innovation while no one knows exactly how much single unit values precisely, every single trade is either confirming current 'established' value or rediscovering new one.
Yes, and it is interesting - why it estimated as "a valuable innovation"?
Also someone were ready to give for bitcoins real goods or to render a real services.