I think he just says that while you can controle hummans' training 100% as a coach, with animals you can never be 100% sure what will happen during schooling, you can only hope that a certain style will keep appearing from the chosed oponent while the animal in train will react the way you hope to. Basically, since you can never absolutely control animals' actions and reactions, your part as a human lowers in significance while the animals' influence on the training increases. In humans you can ask someone to attack a certain way and the other one to defend in a certain style, with animals you can only hope that a trend will keep appearing.
This is the way I get it.