Look closer.
At the very start of the play at
Centre ice Nylander is right beside Sean Couturier stride for stride (that's his man) on the play, because Gardiner is already (as he should be) cheating towards the puck carrier Konecny, keeping himself between the puck carrier and the net.
For some unknown reason Willie abandons Couturier and decides to chase Konecny from behind, this forces Gardiner to suddenly change his Dzone coverage (as its useless both players cover the same guy), and try to get over to a wide open Couturier who scores.
If Nylander stays the whole time with Couturier and covers him and Gardiner stays with the puck carrying its a 2-2 rush. As it turned out Nylander covered no one, and Gardiner was lost in no-mans-land covering no one and it was a simply pass to a wide open player.