The rims not being true are actually hard to "feel" when breaking because the break mounting will move with the flow a bit.
More likely is that your friend has some damage to his rim. Check carefully to see if there is some damage to the wall(s) of the rim that rides against the brake pad.
If you can't see it with your eyes, Give the wheel a spin and sloooowly apply the brakes. If there is some damage or if the rim is not true, it will hit one of the pads and slow or stop the wheel from spinning.