I don't recall if we asked him why he did this, but we did make it clear that he should never leave the house alone at his age. Curiosity-wise, however, we generally let our kids explore the world on their own terms as long as it's not dangerous. And "dangerous", in our view, is understood to be "lasting permanent damage" (doing something that can lead to losing an eye is dangerous, doing something that can lead to breaking a finger is not dangerous).