I don't know that he said it was trash. I remember him saying that he is looking for the "next Bitcoin." Back in 2013 he was acting like BTC was sort of played out and that the next and better iterations of the tech would be better....etc.
I agree with about 95% of what Cuban says.
He is a good guy to follow, I remember he bought a search engine company in the early 2000 and got busted for insider trading but they couldn't prove it. The company went bankrupt but thats what entrepreneurs do, fail and become better :)