From the little information in the article, it looks like this is how it went down:
Jump sent an unsolicited email to Dick, offering $2500 to buy the domain.
Dick did not want to sell and phrased that as "The price for wormhole.com is a firm $50000", expecting nobody would want to pay $50k for it.
Can the latter be seen as a binding offer?
Given the sum of the circumstances, my feeling is that it can not. A one-line reply to an unsolicited email with a price 20x the initial offering is not really signaling a serious will to sell.