If they scored hockey, like soccer it wouldn’t have been a Hat Trick, since one of the goals was an own goal.
That own goal was in overtime, and that was not credited to Marner. Marner had three goals, Thomas Hertl had one goal. The fifth goal was the one you are talking about, so that would have no impact on Marner.
Sorry, correction: The 5th goal in overtime was credited to defenseman Shea Theodore. It’s credited to him, because it bounced of the goalie’s blade.