Breakdowns and mental errors lead to poor production in every NFL city in the league. But it wasn't just missed assignments. We saw plenty of errant throws to open receivers, too.
Execution does go to the coaches, of course. If you're going to take that position, though, you need to take it in the context where this offense has outproduced most offenses in the league during Garrett's time here. The bigger issues have been on the other side of the ball. As for Sunday, yep, the execution was bad. It's one game, with 3 new WRs, 2 new TEs, and two new interior OLs taking snaps in week one against a really good DL. That's not an excuse, because CAR was also playing their first game, but it ought to buy at least a little bit of time for things to gel a little bit. Maybe it's the case that they looked horrible because they're coming up to speed and not that they looked horrible because they suck irredeemably.