Not completely sure but sounds like a bad game of telephone.
Shamans don't have any, other then ES and Totems, buffs for others. So I am assuming, he heard about the old Stormstrike bug.
The -20% nature resist from Stormstrike would stack. Depending on how many shamans you had. 15 shamans all doing Stormstrike on one target and follow it with a lightning bolt crit like in the video below.
Nice 25k crit Wouldn't really help destroy IF though, I don't think.