Is Debian stable a rolling release?

You're right, Debian stable does not have a rolling release model in so far as once a stable release is made, only bug fixes and security fixes are made. As you said, there are distributions built upon the testing and unstable branches (see also here). What is it you're expecting from a rolling release distribution based on stable that is not satisfied by one based on testing?

I guess what you're looking for is Debian CUT, a proposal to create a "Constantly Usable Testing" release. I haven't followed this closely, so I have no idea if this proposal is endorsed or within reach.

As far as I know, Debian doesn't have a rolling release model. At some point no new packages are added to the repositories and only bugfixes are provided. In this case you can upgrade your system to newer release.

Good examples of rolling release model is Gentoo, Arch, ... where in fact there are no formal releases - you simply upgrade gradually.