Actually, I'm not sure the natural 20 was necessary...4e Will is based on either Wisdom or Charisma. And whatever these troublemakers' Wisdom scores, all this hullabaloo speaks of high Charisma.

...And one of the classes that uses Charisma as a classic skill is Sorcerer. Maybe the undead shaman-wizard was just annoyed that a damn sorcerer was getting involved?

(This has been your moment of D&D geekery. We now return you to your regularly scheduled wank.)