I don't know the controls but I don't expect the system should be throwing watchdog messages due to a complete power loss and battery drained.
A watchdog is a general term in electronics for the systems processes are no longer responsive and therefore the system has triggered a reboot, this leaves watchdog message in any logfiles/event logs.
There could be any number of causes but most I have seen come back to unstable mains, electrical spikes or very rarely faulty controls.
PJ is correct you need to look in the log for events around the watchdog also worth checking the voltages with a meter.
Yes, it is considered to the panel that the system has been tampered or is about to be. If armed it will be a full alarm, if disarmed it would be internals only.