That's a community tutorial, however it does appear their panel is very sparse in instructions, when you add the domain you see a nameservers list. They don't even tell you that it's not pointed at them and that you should now configure your nameservers as other providers (like CloudFlare) do. I think you're right, some improved documentation would definitely be good here.

However it's the way I've always done it, because otherwise somebody else could add the domain first... it just made sense to me I guess.