what does it mean to draw by insuff material?

It means that with all the material left on the board no checkmate position exists at all, even if both players would do all they can to create one.

thanks

https://support.chess.com/article/268-my-opponent-ran-out-of-time-why-was-it-a-draw

https://support.chess.com/article/128-what-does-insufficient-mating-material-mean

It means you’ve reached a position where checkmate is not possible because you don’t have enough pieces to possibly deliver a checkmate. For example, if you have a king and a bishop VS a king, it’s insufficient material because a king and a bishop can’t checkmate together alone; another piece is needed. However, if the bishop were a rook, it would not be insufficient material and instead a forced checkmate because a rook and a king can deliver checkmate together.

That checkmate was made possible by black's bishop blocking the king. It's known as a helpmate.

A king + knight are considered insufficient material by chess.com because they can't force a checkmate without help from the opponent.