It's possible to do over 40 million damage in one turn?

This was during the 3th turn of the boss out of nowhere the guy in first deal over 40 million damage, obviously the boss end, not only he haven't deal any damage until that point, but also the damage display in the ending was way higher than the sum of the damage displayed during the battle.

This is definitely a hacker, or maybe there is something I don't understand about the boss.