Assuming he genuinely mean what he say in interviews, Buffet's "Bitcoin is an asset that produces nothing" is probably how most of the older generation of investors see cryptocurrencies.  They'll obviously be more conservative with investments - Buffet regretted not investing in Amazon for example.

Though he's not entirely wrong that the value of bitcoins do somehow depend on how much others are willing to pay for it, I guess what he's missing is that it's intended to be more than a "stock".