Were they real cats? That's pretty bad if so. It's not super awful, it doesn't hurt cats that much when you do that, but they certainly don't tend to like it once they're grown up (it's fine for kittens), and those were big cats, presumably that makes it worse for them.
It looks like they were moving...and yeah I know thats how a lot of vets handle them but they were pretty big/heavy to be held by the scruff like that. Maybe im just more sensitive cuz I have a cat.