Enemies =/= AI. They are talking about intelligent characters and not just stupid NPC trying to attack you with the same moves.
okok for everyones veiwing pleasure please watch.
Stupid characters with pre-programed actions (attack you/walk). If you watch the entire video you will see some enemies in front of the main character, just walking without attack the main character, even if they have the chance to attack.
We are talking about AI (something smart). Using a good AI the character will think logically, attack you in the right time, form a small tactic etc. Something more realistic.
So.. how do you know what type of "AI" they are talking about? All the characters in that video use some sort of AI, they react to player actions, thats what AI is. So the AI that these guys are talking about could be the exact same.
We are talking about Halo, so of course they will use a good AI, just look at Halo 3 ODST. Also, you can simply watch the Vidoc, so you will have your answer.