This is the best way for a student to clarify a technique the instructor has executed - acknowledging he has seen something different, but not assuming it was a mistake. An enlightened, respectful approach.
It may have been a mistake. High belts can know many kata (even from other styles) and many techniques. At advanced years, wires may occasionally get temporarily crossed as he is concentrating on teaching or explaining.
But also, a master will play with variations by design and change a move or two in a kata. So a student who studied at one time may do the form differently from somebody who studied with the master ten years later. He may also teach one student one way to do it, and another student a different way, based on the individual's ability level or body type.
Lastly, after many, many years in the art, one realizes that certain small things don't really matter (but I wouldn't necessarily tell a student that!
) Great technique, balance, power, spirit and tactics will carry the day and overshadow most minor irregularities.