Smoke on the Water in a guitar shop is annoying simply because people playing loudly in guitar shops are annoying and that's one of the most widespread stereotypes of something an annoying person would play loudly at a guitar shop (incidentally, I'd argue that Stairway to Heaven is the more widespread stereotype).

A guitar instructor shouldn't criticize a beginner student for wanting to learn Smoke on the Water, at least assuming it's in the instructor's wheelhouse—it's also okay for a particular instructor to offer a specific curriculum rather than taking requests from the student.