As you can see in the video, Crosby is caught off guard on a bad change and is absolutely pissed off about the way things ended, as he's caught kicking the board a few second later. It felt like the Penguins captain had higher standard for himself.
Clearly, we can interpret that the captain expected better from his team, then a simple mental mistake. The Penguins ended up losing (4-1) for a second time against the Leafs in the last weeks. You can surely expect the captain to bounce back in their next meeting against Toronto.