I would first have to believe that some Boeing engineer was so incompetent that he was unable to read a very basic chart that defines the wire/cable size required to handle x current (amps) over y distance (feet).
He/she and all the peer reviewers, line managers etc. would also be pretty incompetent not to protect the wire/cable (in the old days we used to call it a 'circuit breaker', probably its got a more important name now
).
A plane that has no passengers on it? Requires the full turn out of the entire fire fighting operation? How about using some common sense and despatch a couple of units to fight the fire leaving a complement that is sufficient for normal operation then IF the fire gets out of control summon the rest for assistance. As I said its a knee jerk reaction typical of the world today.
Have you seen how quickly a small aircraft fire can turn into a large one? What's more this one is made of plastic and a new type, that has had well publicized battery overheating problems. Finally it is parked next to buildings and other aircraft.
I would say that they did absolutely the right thing. I also think Boeing will be very grateful that a) we are not looking at pictures of a charred wreck (whatever the cause) and b) there should be little enough damage to be able to determine exactly what went wrong.