I don't think the security guard was an AI. The implication I got was that he was just a collection of canned responses and lines with a simple algorithm to choose between them. Like the voice that talks to you at an ATM machine.
It's been a while since I heard this story, but even if the guard's own responses are canned, it must be smart enough to be able to choose the appropriate response to free-form speech. That still requires AI (not a self-aware AI, I'm using the term in the broad sense to mean "a machine that can respond intelligently to its environment").
In any case, though, I think whether or not the guard is proper AI or not still weakens the story. The whole thrust of the story is a cautionary tale about video manipulation software, and it gains its power by the fact that this software is really very close to being available - heck, I don't know when the story was first written, but out current CG movies are more or less there, all that needs to happen is that the cost/amount of manpower necessary needs to come down. So one of the things that make this an effective conspiracy story is the fact that for all we know, this may already be happening behind closed doors.
So adding the security guard - a piece of technology that is supposed to be public, and is clearly not actually existant, and not going to exist for a few years, if ever (it is a silly piece of technology at best; what's the point of having a security system that seems human? Either pay a human or use a system that feels like a computer). I think that dilutes the story, regardless of how advanced the AI necessary is.
It's as if in the end of
Wag the Dog Robert de Niro would have driven off in a flying car. Not necessary for the film and it would have killed it as satire about the late 1990s.