Ross didn’t salute the American major, I’m guessing out of personal disdain. And then the major yapped some military mumble jumble and activated Ross’ neurons.

Per the comments:

Must feel amazing to outrank your former instructor.

Not only was he mocking him, but implying he never saluted him out of respect.

I like how the German general was made to ask a 2LT permission to address his men.

Has nothing to do with the nazi, especially since the major himself didn’t salute the nazi general. He just nods. Or rather the inclusion of the nazi general should’ve been an indicator that the major was taking the piss out of Ross because the major didn’t respect the Nazi’s rank nor the man.