@B2N2,
Your points are valid, but the manner of the instructor in question - leaning over and making switch selections while not being the pilot flying, is what is wrong here. Imagine your reaction if your car passenger leant over and switched the headlights or wipers on or off. Or adjusted the radio volume without asking.
Some checkers, Captains, TREs get impatient, and/or assume one has forgotten something. A quick example:
My habit when PF on the first flight of the day during normal (jet airline) operations is to start the APU but then wait a minute before selecting APU Bleed on. I then wait another minute before putting the packs on, and continue with my cockpit preparation while this is going on. Some think I have forgotten to make the selections, but I have not forgotten - I am allowing time for the thermal stresses in the APU to reduce before applying load, which extends its working life. And normally, there is no rush to put the packs on instantly.