Well yes and no. Firstly yes he has enough experience to say that based on his understanding, etc. Who are we to judge him for his own opinion?
On the other hand, I see your point that he could make lots of money already, however since there is no tangible thing behind BTC, he shares his thought with a wider audience.
I belive that since the creyptocurrencies (technology behind) can reshape the ecconomy; it could also remove the tangibiity out of necessity to build any ecconomic system e.g. steem? :)
RE: Warren Buffett Not the Dumbest Person on Wall Street