It may be the origin, but it is NOT a correct term today and was something that was always emphasised to me as being incorrect - in fact using "Knots per hour" nowadays is technically a unit of acceleration and is the sort of error I would certainly not expect an instructor to make.
As far as "publicly interfere with the lesson of a fellow instructor." I would certainly agree nothing should be done publicly or in front of his student and I do not think I put anything in my post to suggest that, but he IS teaching the wrong thing, which IMHO is not acceptable.