Buffet is first and foremost a reader and an investor second. He reads A LOT! If he does't like bitcoin it's because techies have failed to explain it or he truly thinks it's not valuable (perhaps he has knowledge of money/currency/banking that most of us dont?).

Not only does he invest in things that are undervalued but they also must provide value. Crypto currencies themselves do not provide value. The companies that make the hardware for mining provide value. Power generation companies that make the electricity for mining provide value. But a crypto currency provides no value by itself, it's just bits and bytes on a harddrive.