No, it's not a bug. If you don't have sufficient material to mate the opponent & your opponent runs out of time, it's a draw.
Bad bug in code?
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No. You were the one with insufficient material. If your opponent runs out of time and you only have your king left, this is not a win for you, this is a draw due to insufficient material. Every chess website has this in its programming. It ain't a bug.
Or not? Maybe not. My opponent's time run out but I still wasn't winner. It was draw! That is new for me. You always learn something new in chess.