"The original run-up in prices could easily be explained as a speculative bubble, and the subsequent decline as the popping of that bubble. But if that were the whole story, then the value of Bitcoins should have continued to decline"
What a stupid statement to make. By definition, a bubble grows, then bursts, then things are back to normal. Similarly, the stock market did not indefinitely continued to decline after the dot com bubble... It is like the author is saying "the price of this stock should decline in the future because it has declined in the past".