I was playing at a tournament and the following happened: I was playing against another player till the "turn" at which when the opponent saw it he went "all in" which I called. Once I have called him, he stands up, throws his cards away on the table, we still couldn't see them and I don't remember if they have touched the other cards, and walks away. At this time the dealer turns his hands and then the river card. I lost cause he had something better than me. My question is: since he throw the cards like he was mucking and walked away from the table, what happens? Are his cards burnt or can he still see the river (as it happened)?
As long as the dealer could retrieve his hand then his hand is live.
A dealer may even go into the muck if he / she is positive which cards were thrown away.
Part of the reason is to avoid chip dumping.
While all-in, you no longer have the option of folding. As long as the dealer is able to ascertain without doubt what his cards are, they are live and he has won the hand. The dealer was correct.