Poor pug, he’s a bit confused.
You’ve possibly (unknowingly) been reinforcing this behaviour, by laughing, trying to calm him down, or otherwise rewarding him with your attention when he engages in these actions. Instead of reacting to his bad behaviour, you should try and reinforce the good behaviour, which, in this case, is sitting or lying down calmly, despite what he sees or hears on TV.
Have you done any clicker training with your dog? I’d recommend getting him used to a marker (like the clicker, or a code word) meaning “this is good, and a reward is coming.” Then, start really slow.
Give him his usual cue for sit, then a new one, like “calm,” “look at me,” “easy,” - whatever you want to call it. Click and treat if he doesn’t move, and stays in his calm manner. Then, start increasing the distractions. Have the TV ready with a paused screen of a dog/horse; click and treat for his calm manner. Do this a lot - ten repetitions, ten clicks, ten delicious morsels - use a high value treat, whatever is his favourite. Mute the TV, and show him a few seconds of moving, but silent animals. Click and treat for calm. If he gets riled up, ignore his behaviour, and take him back to kindergarten - go back to the still screen, and let him “win.”
Gradually, you can work up to having him sit in his calm, neutral position while horses and dogs do their thing at full volume. You can also generalize the behaviour, so he’s not always sitting, he might be on your lap or on his mat, or wherever he usually is while you’re watching TV - when he knows the same rules apply, and he can earn the occasional treat for NOT reacting to the TV, the stimulus gets less and less important to him.
If you haven’t read it, Karen Pryor’s Don’t Shoot The Dog is a great intro into the craft of clicker training. Cesar Millan’s dominance theories (I think that’s the “scruff thing” you referred to) have been discredited.