You can almost hear DeBoer thinking, "We're up by two, so let's just get into the intermission and we'll be in good shape." So they stop being aggressive in moving the puck into the offensive zone, and essentially go into a 5-5 PK, and of course the other team scores. One would presume that after this happens enough, DeBoer would eventually figure out that he's better just keeping the gas on ...... but he doesn't.
It is particularly crazy when the situation exists here where the Sharks were themselves back on their heels and just trying to play their own defense. It's a really bad decision to let the foot off the gas in that situation, but DeBoer just did.