I think bitcoin & other cryptocurrencies are little more than ponzi schemes, but that's kind of irrelevant here. Someone got lucky with their gamble on the coins, and they have generously donated lots of money from their winnings to worthwhile causes. They aren't doing it for fame or recognition, since they have stayed anonymous.

It doesn't matter whether or not you think this donor deserved the money in the first place. As long as the money wasn't stolen, then it simply came from other bitcoin investors/gamblers. It is their loss, and the charities' gain.