So often people get funny ideas about the systems they operate and they talk nonsense. However, sometimes the ideas are based on an in-depth knowledge, that means they know more than the average person. Throughout my career, the tough part was sorting the good stuff from the cr@p It would be good idea to ask your instructor.
Does pressing the foot pedals release the parking / hand brake? This could be a reason for a test.
Maybe the pads get moved to the disc to take up the slack.
It may be that they are suggesting testing the integrity of the pressure line, by making sure the pedals do not sink to limits when foot pressure is applied. This would mean the fluid was squirting out and would probably only happen on one side. A fair piece of airmanship I would have thought.
If pumping the pedal did cause a permanent pressure rise, you're brakes would be on for an expensive landing!!