I'm guessing it jumped into the overflow and clogged the drain enough so the return pump overflowed the tank :fun2:
Sorry to hear about that, hope there wasn't too much damage!
That is why Bean animal style (with oversized drains) is the way to go with any decently sized tank.
You can also set up some float switches to cut the return pump off if the sump level gets too low. But then you would need powerheads in your DT to make sure you maintain water circulation.
By the way, I like the poster you created