Yes, but trying to trap a lone cavalry unit is different from trying to fight a pitched back with 20 units each side. What the AI is doing is basically chasing Orda's cavalry. When I chase a lone cavalry unit, I often get lazy and just select all and click on him. That's what the AI is doing.

I agree, it could be smart and try to box him in, but that is rather advanced tactics. It's actually quite hard to trap a cavalry unit even with several infantry units, the movement speeds are so different and the map is so open (you have to snare them on a map edge or even better corner, but how realistic is that?). Such tactics are also different from those you'd want programmed for a pitched battle.

The fact that Orda can set up multiple flank charges is more worrying, I guess, but I suspect that is due to the extreme maneouvrability of cavalry in the game. Sprint to their flank and turn, you can get a charge in before they have redressed their ranks and settled on the new facing. A human would be more cautious, I guess, but the AI is just trying to catch you as fast as it can.

I wonder what would happen if you did this in STW or MTW? I remember STW had an "insta-rout" mechanic that meant your units would run if you simply trying to lead the superior AI on a wild goose chase. But I don't recall it boxing in lone cavalry units any better. I suspect it still just groups all and clicks on you.