If that figure of $50k is in fact accurate, this would be a CLASSIC case of an inexperienced domain owner who left BOAT LOADS of cash on the table by simply playing a game he/she wasn't equipped to play.
15 Year veteran of the domain business here. You are absolutely right. He left a minimum of $500k on the table.
I represent a few high profile bit coin domains as a broker. The numbers being thrown around right now are crazy. I've been involved in some of the most high profile sales (as owner and broker) in the go-go days of domains and the sales in the bit coin space are right up there. None of them get reported and are under NDA's, but it's the ONLY sector of the domain world that is hitting serious six and seven figs.
One of the domains I represent gets 4 or 5 new offers every day from endusers primarily. Each day we price upwards convinced we're selling too cheap. There's so much money pouring into the space and so few good names.
And to those that think good names don't matter, you're crazy. Just look at the terribly amateurish move that easyco.in did in branding under a .in that a) can be seized by the Indian government and b) is driving a ton of traffic to Easycoin.com. In getting widespread consumer approval of a weird/new/scary currency, a solid .com is even more critical, especially if you're doing ATM's and branded content of any kind.