"watchdog" are meta-processes which are watching for a process step to complete. When it does not do so within the given timeframe, they'll perform a default activity (flushing buffers, restarting processes..or in this case re-booting the AP). (bbox = busybox a set of linux utilities commonly bundled on small appliances)
If this has happened just once you can probably safely ignore. If it's happening repeatedly, it could indicate either a hardware or a software issue -- probably hardware since we don't see other forum posts about it. This page https://www.aerohive.com/support/connect-support/ has some troubleshooting steps and the RMA request form if you need it
-K
