Sure, the monk was, indeed, a vegetarian to the bitter end:

 You turned to stone in Gehennom on dungeon level 48 with 795070 points,
 and 1497 pieces of gold, after 23635 moves.
 Killer: cockatrice
 

 ...
 

 Voluntary challenges
   You were a vegetarian
   You never hit with a wielded weapon
   You never genocided any monsters
   You never polymorphed an object
   You never changed form
   You used 11 wishes
   You did not wish for any artifacts
 

(The alternative, of course, would have been —and you don't want to read this if you don't want to get at all spoiled about Nethack; though this is a really minor spoiler— eating a lizard corpse, for example. But, alas, vegetarians don't eat lizards, either. (And yes, sure, a potion of acid would have helped too.))