Was it a wrong technique, or a variation in the kata?
And whether a student should pass in that situation depends how you look at both the situation and kata. To me, if the student learned what they were taught, they probably ought to pass (within reason). If the instructor taught something actually wrong (mechanics that are harmful) that's not the student's fault, but should be addressed by the instructor's peers, as best they can.
If the instructor is just teaching a significant variation in the kata, that's only problematic if the student changes schools. It's "correct" in the context of the current school, so shouldn't really bother anyone.