The Spirit of Yahweh came mightily on him, and he tore him as he would have torn a kid; and he had nothing in his hand: but he didn't tell his father or his mother what he had done.
Even though God strengthened him, Samson used that strength for his own purposes, not to fulfill God’s will. Note David’s very different reaction to God enabling him to kill a lion and a bear in 1 Samuel 17:34-37.