I think the argument is that for it to truly be AI, it would need to be able to react to new situations that it isn't trained on.
Like everything it does now is just picking the most likely thing out of the things it was trained on, but with no thought to the current situation.
For example, AI powered self driving cars can't really make decisions like, "hey there is a child playing with a ball on the side of the road, it's not a threat, but I'd better pay attention to where that ball is going". It will just not do anything until it is on a collision course and by that time, it may not have enough space to stop in time, because it also can't really tell the condition of the roads.
The AI as it exists right now basically only knows about the moment it is currently in and the moment it just left. It is not looking toward the future and thinking of possible outcomes and plans of action like we do. It doesn't attempt to identify situations until they actually happen so while it can react faster than a human, humans can make it so they never have to react at all.