Is this drawn?

 I had a curious situation at Street Chess today. After a very up and down game between two relatively new players, one player resigned the game. However, the player who resigned had a K+P on the board, while the other player only had a K. Of course I was only half paying attention, and initially assumed it was the other way round, and commented that the player who resigned could have drawn the ending. It was then pointed out that the player who resigned could not possibly have lost the position, as they were the one with the pawn.

Why did the player resign? Simply because he thought his opponent had played well enough to earnt he full point. But after further discussion (and and an explanation of the rules), the game was recorded as a draw. Now while this was the correct decision from a practical point of view, was it the correct decision from a legal point of view?