Literally the the first paragraph
He didn't actually say or imply what you think he did. In fact a later part of the comment ("10/month? That's 30 videos in HD max. $100? 300 videos in 4K... etc. ... or whatever.") clarifies that he meant what he wrote and it is something quite different to what you're picking out.
My point from the beginning was that $100/month is not enough to host a successful channel on YouTube. You absolutely can do it on vimeo, self hosted jellyfin or similar. Plenty of options around. It just get extremely expensive if you're serving content to hundreds of thousands or even millions of viewers.
You can probably start at $10/month with a hetzner shared instance and 1tb storage and unmetered 1 Gigabit Ethernet. Gonna be fine for ~2 simultaneous viewers
I only addressed the storage first because his idea was so far outside of a realistic price. Storage cost is a rounding error on the invoice if you're serving videos to consumers with views as a semi successful YouTube channel gets
I think that is still overcooking it. Peertube has a FAQ on the subject [0], going off that it's probably achievable to have 1,000 concurrent users at ~$50/month+storage. Not commercially advisable, it is pretty obvious that everyone in the game ends up going ad-supported and that makes sense to me. But YouTube could in support something like that for small channels without too much trouble. The issue here for the median channel case doesn't look like costs in the >$1,000/month range as much as foregone revenue and operational complexity. The vast majority of content creators don't get hundreds of thousands of views.
[0] https://joinpeertube.org/faq#should-i-have-a-big-server-to-r...
He suggested $100/month for 300 videos and noted that he was experienced in content creating.