As the Predators were changing, David Legwand decided to just flick the puck toward the net. It was a harmless play, one that happens every single night in the NHL. Nine times out of 10, a goaltender will stop the "shot" (if you want to call it that.)
Unfortunately Dubnyk didn't. It wasn't entirely his fault, as the puck seemed to take an awkward bounce to his left as he was sliding to the right. But still, that's a goal you just absolutely can not give up at this level of hockey.
As for the Predators, that's the kind of bounce they haven't been getting lately.