Spectrum is Charter's branding. And with Charter buying out TWC, they seem to simply be unifying the two brands under the name Spectrum.
Charter also bought Bright House at the same time as Time Warner Cable. They are all being brought under the Spectrum name, which was and is Charter's pre-existing name for their cable services.
This is not the scenario at all that "rebranding" invokes. Especially not in the context that chimeracoder uses it. See ssharp's post [0] for an example of what the typical interpretation would be.