When black runs out of time the game immediately ends and white is granted the best possible result that could be obtained from the current position when black’s time ran out. Because in your example white only has a king, the best result white could obtain is a draw and the result is drawn up as that.
I had a discussion in some page where in the scenario;
1. Black have rook and king
2. White only have king
But black runs out of time and white have 2mins
Is it a draw or white wins?