It's a lot harder than you'd expect, which is part of why I don't have much of a problem with this particular choice of words. "Retarded" could probably be replaced with whatever the current medical equivalent is (Developmentally disabled? Mentally handicapped?), but there isn't another medical term for "autistic".
One thing I struggled with in my more complex post was finding a phrasing for what he said that didn't use his terms and wasn't inherently derogatory towards the 'lead actor'. He's trying to convey two separate concepts with those two words.
- The player character may be physically fit, capable of running, jumping, and lifting things, but they're incredibly limited in how they can interact with their environment, through no fault of the player.
- The player character may have the capacity for eloquence in limited contexts, but they're incredibly limited in how they can interact with other people, and they're prone to behaviors around other people that would be rude at best. A player character cannot and likely will not uphold basic elements of courtesy that come naturally to most people raised in society.
The language of mental illness makes sense here, because it's not a problem that can be solved by education alone. The interface of a game creates fundamental challenges in accurately simulating reality, and the medium itself (one with goals and rulesets, played for a person's entertainment) discourages any kind of real socialization with the AI. Other words (sociopath? idiotic? maladjusted?) only have use as insults or descriptions of poor character, and he's not trying to insult singleplayer games.
If his words caused this much confusion, it's obviously worth finding another way to describe it. But I do think they precisely hit a meaning that would be hard to reach otherwise. And brevity is important here, considering the thrust of his talk is about multiplayer, not singleplayer.