I had always assumed that the extraneous information was part of the test. You have to know/understand the concept well enough to know that the information was extraneous.

From what I remember of school, extraneous information was rarely included and the teachers who did add extraneous information seemed to do it maliciously.

There was one math class at a private school I attended that was the exception. The textbook had identifying relevant information as part of several chapters.