This was a ceiling fan installation, Randy, a homeowner job, I'm sure. IMO the problem was pulling the short varnished-cambric covered wires into the box. Varnished-cambric is usually OK except in light fixtures where it gets brittle from the heat. I usually go in the attic and cut back to unheated wire, install boxes in the attic, and pull new wire to the ceiling fan. In this case I rewired the second floor with 3 circuits from the basement distribution panel.
I think the overcurrent protection was OK (since I did the service). I use QO because they pop the best, IMO. I think this one did a slow burn under 15 amps until it finally popped.
Dave
P.S. A dictionary near the PC can be useful.
