Well duh, what a surprise
"The techies claim to have experienced a greater rate of accuracy using the game data to train their AI than relying entirely on the real-world stuff from CamVid."
Game data is obviously great for AI training. You have a virtual world created by a computer used as training grounds for another computer. Advantages ? No clutter, no useless noise, and faces are polygons with textures stretched on. No pimples, no puffiness under the eyes, no 5-o'clock beard. The only things shown are the things that have been calculated. No wonder it's easier for a statistical analysis machine (what we currently call AI) to recognize and classify.
Unfortunately, Real Life (TM) is messier than that. Granted, it may be advantageous to train a not-AI on such data before turning it loose on actual, real images, but there's also a chance that we are just fooling ourselves into thinking that we are making this work. It's the Hall of Mirrors effects for the Mentats of Dune.