It’s great that someone has finally fingered out how they did it.
I think you “nailed” it. You seem to have your finger on the pulse of prehistoric times.
Maybe it means “Goomba at 4 yrs. old. Goomba at 7 years old. Goomba just before the bear ate him.” We had the same type of markings in my old farmhouse before the bulldozer ate it.