Just from a brief read, Tantrum is based off a Data Spike action which includes a damage resistance to begin with, combined with the Tantrum statement that even if a single box of matrix damage is scored...
I think you're spot on that you would resolve the theoretical matrix damage, if there is 1 or more boxes of "damage" after the "damage resistance" test (As this action doesn't actually do any damage), then you would have the effects of nausea including the incapacitation effect if more "boxes" are scored than Willpower (The more part being important as ties go to defender)
Though an argument could be made that only Hot Sim is at risk for the full blown incapacitation as Cold Sim is supposed to protect you from the worst part of harmful code.