I have a newbie question on nameservers @ cloudflare. All these while I have been using the nameservers below for my domains
ariella.ns.cloudflare.com hugh.ns.cloudflare.com
But tonight when I added a new domain via runcloud and then another one via cloudflare, I was asked to change to new nameservers
Is this common?
Yes, the nameserver combinations are unique to your account. So when you add them via runcloud, they will be different as runcloud has been assigned other nameservers by Cloudflare.
You can read more about the history of why they are 'names' here -
https://blog.cloudflare.com/whats-the-story-behind-the-names-of-cloudflares-name-servers/