He was putting the card out, wasn't sure if he already burned so hesitated and pulled the card back, then realised he hadalready burned so he put out the card. Then Seiver started joking about it and they all laughed.
That's what I think happened.
I think he accidentally grabbed two cards and then put both back. The upper one went on a turn and the bottom one is going to be burned before river anyway.
I don't understand what happened. Clearly the guy didn't just switch around the order of the top 2 cards in the deck or there would have been more of a fuss caused by the players. But at the same time it seems almost like that's what they are implying happened. Don't know what I just saw.