I dont think the competining motivators method would work well for when the dog runs into the cat and no immidiate supervision is present, or what if he is not hungry? Wheras the E Collar makes it about the cat and the dog (you hope) no third party. Its proven that a strong aversive is more likely to stick in LT memory so for this sort of thing Id prefer it.
I think you can debate how he worked the dog with the collar (if he was actually using one) and set the whole situation up. I think that could have been done better.
Have run into several cat killer GSDs of late..seems to be common with this breed.
Such shy animals are in all circumstances an encumbrance to their owner, who must be ashamed of such a dog, and a disgrace to their race. Under no circumstances whatever must they be used for breeding, however noble and striking they may appear.