He focuses on one usecase of bitcoins, while completely ignoring the other. Yes, bitcoins are being bought with the expectation that their price is going to raise in the future, and this clearly is not sustainable. But they are also being used to transfer money between individuals. There the price fluctuation doesn't matter that much (if the merchant immediately converts into USD).
Lately there have been many people saying bad things about bitcoin. I think those are people who had bitcoin on their radar a few months ago but didn't invest. And now they are just grumpy because they missed the opportunity.