My 2 cents:

Aaron's claim: Y is true because: If X then Y.
MrVoluntarist's argument: If X then Z; Z is false; therefore not X.  Thus Aaron's argument is invalid.

Note that MrVoluntarist's argument doesn't prove Y is false; it simply proves that Y is true because: If X then Y is not a valid argument.  If MrVoluntarist had said that Aaron's claim was Z, that would have been a strawman.  But MrVoluntarist simply showed to Aaron's satisfaction that X was false. That is not a strawman; that's simply pointing out a false premise.

X is If an action is violent, then it is wrong.Y is The violent act of shooting trespassers is wrong.Z is The violent act of fighting in a war is wrong.''