I think you're still missing it.

In coding, ! is equivalent to formal logic's ~. It's a negation. Therefore:

%ismember (foo, @bar)=0
is equivalent to
!%ismember (foo, @bar)

See it now?

EDIT: Nevermind! He's fixed it.

Yes, however, in murphy's ORIGINAL code, Concusion was checking to equal 1 not 0. Hence the confusion.