[wizofaus]

It could if it had enough training data that demonstrated "I don't know" is a perfectly valid answer to a question. The risk than is that it answers "I don't know" even when it is actually capable of providing a useful answer. In fact I've had it do that before too - not exactly "I don't know" but vague statements that aren't particularly helpful, when it turns out with the right prompt it "knew" exactly what the answer was.