[Sans Peur]

Sounds like the terminal stud on the starter broke internally and was probably barely making a connection. I bet if you had felt the solenoid during starting it would be red hot. After it started there would be resistance from the heated connection consequently dropping the voltage going back to the batteries and systems.

It happens, rarely, but it happens. I would not sweat it to much. Max I would do is maybe buy a rebuilt starter and carry it on board as a spare. But i sometimes am far away from reliable mechanics and parts so I go a little over on carrying replacement stuff.