I would bet quite a bit that he was just plain misinformed rather than raising the bar. Many people refer to this exercise as "treading water" or "floating," although neither term is used in the standard. Since they have in their mind that the exercise is named "treading water," then, by golly, they had better be treading water. According to the standards, the only real requirement is not drowning. I used to tell students that if they drowned during the exercise, they automatically failed the class.A good example was one instructor I assisted requiring OW students to do the 10 minute float and not allowing drown-proofing (or else they "fail"?).
I would also bet the overwhelming majority of instructors are mistaken about at least one standard, and many are mistaken about more than a few. What happens is that whoever conducts the IDC that trains the instructors teaches them to teach certain skills the way the trainer does it. When they become instructors, they teach the way they were taught, and they get the idea that every step is required. The actual standards for most skills are written intentionally vaguely to allow different acceptable methodologies. A good example is the alternate air exercise, where the wording allows any of the normally accepted methods of sharing air.