On our SN (#68) the bow thruster and Foc furler are hard wired with no fuse or circuit breaker (diruptor). Real men don't need them ;-)
The 100amp fuse (mine is Blue Seas pop-up breaker style) is for the anchor windlass.
The main 12v power only kills power to the relay switches at the helm (same as turning off the "joy stick" breaker on the main DC panel). So when you say turning that off still left the BT and furler live, you were probing at the BT solenoid line terminals (not load), right, and the solenoids were actually inoperable from the helm switches. That seems safe enough, that is, you couldn't accidentally operate them from the helm.
If you want to actually kill the power to the bow thruster and furler, just turn off your main battery switch - remote twist handle in the port cockpit lazarette locker, next to the helm. If you have a fuse in the main battery feed, that's your safety for a dead short at the furler/bow thruster. If not you'll have one heck of a cabin heater.