That's likely due to a cocked pad, either due to an improper install or the caliper not straddling the rotor correctly, or possibly a bent pad. Just think about it a bit and it will all make sense.
The pad wasn't just touching in one area, it was NOT touching in the rest of the area. That cannot happen unless something is mechanically wrong. And surely you would have noticed a bent pad prior to the install, as the pads are usually shipped face to face.Even if not shipped that way, it is common practice to check them that way.