Is this subnetting video incorrect? I don't get what he's doing here.

https://www.youtube.com/watch?time_continue=316&v=uyRtYUg6bnw

Is he doing some kind of "classful" subnetting? Because from what I've learned it's only CIDR that counts, classes have no meaning since 1993 (other than the private ranges). Also subnet calulcators online shows the results I would expect ie ignoring classes & just counting the mask. Or have I completely misunderstood everything?

This video has many views & high rating so what am I missing? What is he doing. Thanks