Wow, these guys are way too certain of themselves. And this isn't direct evidence of anything except polarization. Anything beyond that, be it gravitational waves or what that says about the first moments after the Big Bang, are indirect.
Science is a process of discovery, and we need to be open to alternatives that are not disproven. The expansion of the universe is a great example of this. Everybody "knows" that the universe is expanding and that this indicates a Big Bang is the most likely origin story. But technically, all we have observed is that there is a correlation between distance and red shift, assuming that absorption spectra are constant over space/time and light doesn't chance frequency in travel. We have not actually observed that distant galaxies are actually moving away from us. We literally have no direct evidence that the universe is expanding. It's a theory. Not proven fact.
To put a more fine point on it, we know (can demonstrate experimentally) that relative motion is _a_ cause of red-shift, and we observe red-shift. We have not, in fact, observed this relative motion on scales large enough to demonstrate universal expansion. This is an indirect measurement believed to be reliable, but not proven. We can only observe relative motion on very close things via parallax, and we've found that some things are coming towards us, so relative motion locally is not dominated by expansion. We rely on the theory. It could be wrong.
A viable alternate theory is that light gives up some energy while traveling extremely long distances, which shows up as red-shift. Where does the energy go? It could be the source of energy for the CMBR. It could go somewhere else. In any case, as a theory, it explains the red-shift just as well as expansion.
Another viable alternate theory is that the absorption/emission spectra of atoms differs with space/time. Perhaps atoms farther away or longer ago created and absorbed light at lower frequencies, this making older light appear red-shifted by current frequency comparisons. This theory is even harder to test, but just as good at explaining the observations.
As a scientist, remember the difference between theory and proof.