I'm guessing two different 'things' happened. One was a cap that was installed cockeyed and the rotor tip gouged the side of the cap.

The second was that arcing at the center electrode. I have seen this happen when the condenser was of the wrong capacity in the old point system, which I'm thinking you do not have and secondly, when the coil is reverse installed. Also, if there is a starting resistor that is supposed to be in the system and was either left out or gone bad. Then there is that old bugaboo - just one of those mysteries. Happens once and not a dang thing that happened before or ever will again