The most damage a 9th Martial Artist should be able to do is 1D6+ the Stat mod for a single hit unless he has loaded up on Sneak Attack dice. Even then I'd be hard pressed to believe more than 4 Sneak Attack dice are available. He would have a Threat range of 19-20 but that would bypass Vitality and go directly to Wounds (which may have happened as I don't know the situation it occured under).
The only other possibility I can think is he used an Action Die to add to the damage and the AD kept exploding (which is possible but law of averages says unlikely).
From the World on Fire where the Martial Artist is located:
Wuxia I: At Level 8, your horizontal and vertical Acrobatics/Jump
check results are no longer limited by your height. Further, the
distance you travel when making a Jump check increases by 50%
Wuxia II: At Level 16, the distance you travel when making a
Jump check increases by an additional 50% (for a total increase
of 100%). Further, you are considered to weigh only 1 lb. when
determining if a surface or object can support your weight.
So are the fighting classes that badass? ... They are badass but not by the level you are thinking. They can do lots of damage over a long period of time and stay in the fight, on the average, for a long period of time. But the beauty of the Crafty system is that all it takes is one activated crit with a high enough damage quotient and any character, Special/PC or NPC, is done for the fight and possibly permanently.
So consider if you had gotten an attack off first that was a Threat, you activated it to make it a crit, and your damage bypassed all the Martial Artist's Vitality and hit his Wounds. He goes to 0 Wounds and falls unconscious or he goes to -10 Wounds and dies. Just stuff to consider.