He did what he needed to do. He didn't turn the ball over and made enough throws for the offense to score some points. The pass he threw on the TD was a great throw, with great coverage. A good throw almost always beats good coverage.
What impressed me the most is he doesn't lose confidence to make throws, something you want to see in a young QB. It would be better if he was more mobile but he is who he is at this point. But, as you stated, you'll play another team that will shut down your run and Petras will need to show he can move the ball consistently. Ultimately your season hinges on his development and possibly the development of your tackles. When teams get to him he's not going to evade the sack so you have to keep him clean as much as possible.