Not sure if he did everything all by himself.

Regardless, it was bound to happen sooner or later as youtube is getting older.

It's just a 2 billion limit crossed, 32 bits can count up to 4 billion. Afterwards, they certainly don't have to change to 64-bits, just add a few bits more.

there's no reason to pick any number between 33 and 63

If you do it at home, for your 10 videos, there isn't. At youtube scale, they certainly can benefit in having different number of bits in storage and transit and in the CPU. Only on the CPU, and only if you actually want to use the value in calculations the 64 bits is best step after 32. See also discussion here: https://news.ycombinator.com/item?id=8691291

And don't forget there are multiple copies of the same video there.

My understanding is that the original is the only video that has broken the 32 bit integer barrier though, right?

I think the point is that the number of people who watched the video on YouTube is even larger than the number associated with this copy.