The teacher cares about the system composed of the poem and its cultural context; the student cares about the system composed of grades, tests, and credentials which will eventually allow them access to the work they want to do. The meaning of the poem may or may not be confusing and arbitrary, but our hypothetical engineering student is actually trying to play "guess which subset of all the possible meanings the teacher will accept", and is thus frustrated less with the actual poem than with the system which presents understanding of the poem as an obstacle toward the student's goals.
Sure, but I bet the only reason you remember the disagreement well enough to comment on it is that it was a teacher you had to disagree with. People talk all kinds of bullshit and it generally doesn't mean anything, but when someone with some authority talks bullshit, that's frustrating because you have to deal with it anyway.
