So they are - apparently - cheating... Which is not exactly anything new in MP games....you realize he's talking about singleplayer, right? :p
That's certainly peculiar. I've never had that happen to me before. Maybe the slow-mo mod may have messed a bit with the AI, inadvertently?I don't think so - the slowmo is only a config file mapping the Q key to a console command to set the game speed multiplier to 0.3.
It happens in CoD4 too, if you look hard enough you'll see the enemies use aimbot like the helicopters. Several times I have been sneaking up stairs only to have the enemy shoot me time I come out. You can also see the aimbot if you are fighting enemies follow me perfectly through boxes. :p