blurred vertical line that moves

[Your Computer]

Some games implement something similar to vsync but not exactly. This is why in some games you don't need to enable vsync. The blurred line is called screen tearing. This can occur when the FPS is greater than your monitor's refresh rate. The game by default limits the FPS to 60, which is a common refresh rate. There is also the possibility that the graphics card driver is enabling vsync in the background regardless of whether or not vsync is enabled in game: this is probably why your friend can play without having to enable vsync.