Not concerned at all here.
The things to keep in mind are that:
-He has some rust to knock off because he did miss some time due to the back issues. However, he appeared fine, took hits, and there have been no reports of pain or anything this week following the game.
-He has a new OC and that takes some adjustment. And he doesn't seem to be having the same challenges Eli Manning has
-San Fran is still a good team. No, they weren't playing against Seattle, but this is still one of the better teams.
What I saw was just "one of those games". Lots of big name FNL players didn't look their best Week one and that happens every year. I expect Romo to settle in and for the new OC to do his thing in getting lots of opportunities. The Cowboys don't really figure to be a team that can dictate unto their opponents much this year so there will be passes made and some in catch-up and garbage time.