A few people tried to play this card some years ago, and the league went ahead and altered the rule to make it so that as long as the player keeps moving forward himself, the puck's movement along that flight path is not itself grounds for having a goal disallowed. It was a very sound idea. Before they did that, all kinds of people tried to nitpick every individual deke and it was a time bomb that figured to go off at some point in a key game. At the very least, it was going to give talking heads something to natter on about forever.
In this instance, Kane slowed but he did not stop, and he did not begin moving backwards at any point. The new rule takes care of any lingering doubt about this one. It's legal, even if the player clearly pulls the puck backwards during the player's trajectory forward.