Attacking Unconnected Provinces

[thejeff]

The AI knows things it shouldn't.

This is why it will occasionally declare war on you and drop remote attacks and seeking arrows on you while you have no idea where it is.

[Gandalf Parker]

Keep in mind that the AI is another nation in the game.
In fact, its 3 nations. Indepts, Spec1, and Spec2. Those "nations" are susceptible to the same things in the game as everyone else. So even the Independents will get random events which attack their locations.

So in that way, YES, the AI will attack unconnected provinces.