Funny you should say that. Reason being it's a load of nonsense. I've played numerous FPS games where the AI reacts differently depending on the difficulty setting. For starters, take the Call of Duty Series. I've played most of them from day one and one thing I always notice is that when you up the difficulty, the AI characters all become a lot more accurate with their shooting. In other words, the AI is acting differently.
What you're seeing there is a small variable change.
"More accurate" does not mean "different behaviour". That's as silly as saying "faster" or "harder" is "different behaviour".
But feel free to believe whatever you want.