It doesn't appear to be a rebranding, but an upgrade or a rewrite, since the site mentions the first two points (that I checked):

https://cloud.google.com/cloud-build/

"Set up triggers to automatically build, test, or deploy source code when you push changes to GitHub, Cloud Source Repositories, or a Bitbucket repository."

https://cloud.google.com/cloud-build/docs/configure-third-pa...

I looked at Container Builder before and, like you, was not impressed, but this is something else.