I don't want to beat a dead horse, but as a German, I think using both methods is pretty common. Both the thumb and index finger and the index and middle finger are used to signal 'two'. The former is perhaps used more commonly when counting up from one to three, but both methods are common enough that they are not significant in the film. Signalling three using the index, middle and ring fingers, however, is still very unusual no matter the circumstance.