He is not completely wrong, but we could say the same about gold for example.
His vision about investment is like "whatever generate cash flows", and bitcoin obviously does not have any cash flow, but it do have a worth based on asks and bids. So it is gold and silver.
Yes, what he said does makes sense, bitcoin is a speculative asset, we can't deny it, however, I don't think that speculative asset like bitcoin can have a staying power of almost a decade now. If people doesn't see anything from any asset, it will simply die down. But bitcoin is challenging how we look at an asset and that is what Warren Buffett doesn't understand because he came from a old traditional way of investing.
Did he say that to Soros though? because there are news circulating around that Soros finally decided to invest on crypto, why did he change his mind? I don't have any idea but Warren seems to stick with his notion that bitcoin will suddenly die down but so far we are still alive and breathing.