...Some sort of coincidence that a rarely required system is used, and it's supply CB "pops". Suspect that is not a coincidence. Whether it popped immediately (in which the crew's account does not tally) or later (with Altn Gear Extension being ON for some time?).
This is where my suspicions lie. The Alt gear ext DC motor and actuator have a limit of two duty cycles followed by a 10 min cool down. Normally this would be no problem as the actuator takes just over 5 sec to run at which point a limit switch shuts it off. The QRH directs the crew to leave the switch in DN for the remainder of the flight. So if something precluded the actuator from moving, it cannot reach the limit switch and it will attempt to run continuously. Because it has a duty cycle, you would eventually expect a circuit breaker to trip. It could have tripped well after the crew attempted the unsuccessful ALT extension for all we know.
PS You of course meant to say "Accidents are
rarely simple / one cause."