Looks like a combination of rim wear and overinflation. That's definitely rim wear and the way the whole rim seems to be starting to sag outward is not good. Our 300# team touring with full luggage runs 115 lbs. on 28mm tires. Rim manufacturers inflation pressure limits approximately coincide with those recommended by tire manufacturers. Running a disc on an old worn rim means that you can't feel the rim pulsing in the rim brake lever, which is how I tell when it's time to retire a rim.