Attendee of a British-style boarding school in Australia in the mid-60s here. The vegetables were cooked so long they were virtually indistinguishable; that grey-green splodge could be peas, brussels sprouts, broccoli, spinach, broad beans or on a bad day mashed potatoes (made up from the vast vats of DEB potato powder in the “kitchens”). Everything - veges, beef, dessert - was boiled for hour after hour before being deemed edible. The plate was invariably awash with this thin grey watery paste that flowed off the alleged food. Why, I have no idea, except that’s the way it was always done I suspect.
How we grew past about 4 feet tall I have no idea, there could have been no skerrick of nutrition left in anything there.