Jusforfun

One of the known V6 3.0 TDI issues is the little swirl flap linkage arms. As they are over the exhausts they stretch with heat and use. It means they don't achieve the full travel and give the symptoms of swirl flaps not opening fully which is an expensive replace. They will not last longer than about 75000 kms. A simple if not impossible click to fit. The job is simple but human fingers will barely fit in the gap.
If that is the issue it happened because the tester revved the car foot to the floor during the test which is something you don't normally do. The light goes off after a couple of days... Just one of the possible CEL causes.
On another CEL I replaced my throttle body only to find the old one was barely dusty inside. Just enough to make it not fully open I could have cleaned it myself... next time

Edzzed

Just an FYI, I was driving down the highway and stepped on the fuel, I had zero power. It would accelerate but in limp mode with the CEL illuminated. I pulled over and shut the engine off. I then restarted the car and no light. all was fine and ample power. On reading codes I had a boost code. Turned out a crack in my boost hose caused it. I also get the intake runner code sporadically. Audi is 82 miles from me. One day I will take it in as it is under warranty.