for us decentralized currency is merit but for buffet same merit is demerit as no govt or central bank back it so it is just speculative asset.
Prices of bitcoin are so much volatile and no doubt sometimes it is manipulated also, so this one may be the 2nd reasons for him to bash btc.
But the way he hate shows he is confident of his opinion and do not want to give time to crypto market get stability as it is just beginning and we need to do more work here for adoption like fiat and gold. So there should be criticism instead of having arrogant view on btc.