The problem stems from the fact that we can have what Robert Shiller calls naturally occurring Ponzis, that is, financial bubbles that form without the manipulators baton but from finished natural market forces and with one persons expectations feeding into anothers, says Basu.
The quote defines a "natrually occurring Ponzi" as a thing sold at market that forms a bubble. This could very well apply to Bitcoin, as Bitcoin has been in bubbles and may be in a bubble, but that has absolutely nothing to do with Ponzi schemes.
bubble != Ponzi. "Ponzi" has become a catch-all term for "something financial that I don't understand but I'm still suspicious of." And such people are going way out of their way to fit the word "Ponzi" in here somewhere, even if it's completely unrecognizable from anything Charles Ponzi ever did.