Uneven wear on brake pad
It is not unusual to see brake pads worn like this.
In order to keep brakes from squealing pads are often set so that they hit the rim at an angle.
This means that the brake pad will wear at an angle.
That being said - it does look like someone was a little over enthusiastic on the angle of your pads.

The arrow indicated the direction of wheel spin.
The brake pads are pictured at an extreme angle to make illustrate the point.
Pads should be &quot;toed in&quot; just enough to stop the noise and no more.