One of the meanings of the verb to overlook is "to provide a view of" (the chateau overlooks fields of olive trees), when it gives you the possibility of seeing. The other meaning is "to fail to notice," (I have overlooked the key fact), when you lack the possibility of seeing.
How can one term include two opposite meanings?
(This is my analysis, surely I may be wrong.)
Interestingly, there is no contradiction if we consider the real physical meaning of this verb—"to see above." When you say "I could overlook the whole village from my window," it means you could see above the buildings, trees and other structures in the village. It actually does not say that you could see the structures themselves, but we imply that—if you could see above something you could see the object itself.
So now this meaning does not contradict with the second—"I have overlooked his car in the road," which means I was looking above the car, and that's why I didn't see it.
