I think the issue here isn't exactly what you're catching. You're trying to explain what happened logically.
"Why did she do so much damage? how many levels up was she? what was her items? what were their items? How does that translate into a champion skill level and gold lead for advantage?"
when the main issue is something you've already pointed out yourself as well. You've seen other champions able to generate this much damage, so how is it special?
Rubick is trying to point out why it's special when you're focusing on all the other issues that literally any other champ can acquire with a decent snowball. you're missing the forest for the trees.
Camille started the video at ~25% health and then killed 7 of the enemy team in the span of 54 seconds from the time of the first engage. the fight started with camille in baron bit, went to top tower tri bush, spanned all the way to top inhibitor tower, around mid inhib, down past bottom inhibitor tower, and ended back at bottom inhibitor. netting 7 kills in almost 50 seconds flat and spanning a distance almost the whole length of SR to boot.
meaning Camille somehow demonstrated an ability to shield and heal enough to kill 7 of the enemy in less than a minute while starting with 1/4 health, receiving no healing or shielding from allies, and being able to move a distance of almost equal to the entire length of the map WHILE being able to take enough time to murder the ENTIRE enemy team 1 1/2 times over.
some champions have good enough sustain in 1v1 fights to do this. some champions kill fast enough to do this. some champions can move fast enough to do this. The point is that camille did ALL THREE of these. She self healed and shielded herself through 7 consecutive fights, winning all of them, and flying through the map at a pace that
could probably only barely squeek out if he_ just walked the whole time_. Mordekaiser could probably only make that run in the same aount of time if he never once stopped to attack literally anything. Camille killed 7 champions while doing it. Morde could have sustained through it just like her if he was just as fed, but he couldnt do it nearly as fast.
Vi could do it almost as fast as camille, but Vi has no sustain. She would have died before the end. exact same goes for lee. he has the damage and mobility, not the sustain. Camille hits really hard, sustains and shields really well, and moves really, really fast. items and levels dont matter. it's all in the kit here. that's all you need to know.