Certainly there would have been methods available even then to either overlay changes (~cels) or exactly reproduce a base image (xerographic). I'm just impressed even using tracing he didn't just 1:1 reproduce the same scene, tiny variations exist (nose shape, left fist, V-neck shape etc.).
Dogs are way more cognizant of body language and tone than most people realize. You can talk gibberish to them, but as long as you include their name (which they can recognize) and then use a positive, loving tone or a negative, aggressive tone, you can communicate nearly anything.