It's kind of funny, but on one hand, that statement is probably the best thing a libertarian reader could imagine hearing from Yellen. That's how I read it at first, and was thinking, "wow, that's pretty radical for the government to intentionally take itself out". Yet, upon second reading, I think the intention was probably more to cast Bitcoin as a wild-west, do-at-your-own-risk, good-luck-to-ya type of asset to work with. I think the message was meant more for banks and investors. The real subtext being, "if you lose your shirt, get defrauded, or there's large scale tampering, don't come crying to the Fed".