I do not think it is unbelievable that a cryptographer would not have heard of Bitcoin. Bitcoin is just not that interesting to cryptography researchers or professionals; there is a polynomial time attack (for a vague notion of what it means to attack Bitcoin), no security definition, and a requirement that the honest parties scale their work with the work done by the attacker. It is almost certainly not the case that Bitcoin was created by an expert cryptographer or by a team of experts; one need not look any further than the original Bitcoin paper to see why (no references to previous work on digital cash? no reference to security multiparty computation? an expert cryptographer would most likely have mentioned at least some related work).