Why did this guy quit?

He might’ve been upset with himself for blundering and losing the exchange. At your level losing the exchange shouldn’t be a big deal. It’s recommended to continue playing until the game is over.

Congratulations on your Flawless Victory!

It’s obvious why your opponent quit.

He was completely lost.

Good thing your opponent was honorable.

He didn’t want to drag out the lose and force you to demonstrate the proper winning technique.

He probably already knew you can convert the position.

Good thing your opponent quit when he did.

Otherwise, his reputation would have been tarnished.

Playing on when your completely lost with no compensation is bad etiquette and considered very rude.

This is why your opponent quit which demonstrates to me that your opponent will be great in chess 1 day.