A ballast resistor drops voltage from around 14.2 to 9.5 VDC to increase ignition component life. I does that by loading the circuit and consuming voltage but this voltage drop produces heat. A ballast resistor gets hot, hot enough to burn you pretty quick.
I will go out on a line here and guess you either had the key in the run position or some failure let the BR sit there and cook (worse if points happened to be closed) for 20+ min. You can bet the coil was hot as hell too. Check the coil for
oil leaking out or a bulged case. I would carry a spare if it is not bad today.
Then the jumper cables tried to dump high amperage into a dead battery and you hit it with the big amps from the starter when she
would crank over. Add maybe a poor connection internal to your bad disconnect switch. No surprises here.