Hello!
...and what you would do/say?
Do you know, where the unit "knots" has it's origin? See here:
Knot (unit) - Wikipedia, the free encyclopedia
So, as a matter of fact, "knots per hour" comes very close to the original meaning of the term! And regarding the question: No, I would never publicly interfere with the lesson of a fellow instructor. And especially not regarding such an unimportant matter.