I don’t buy it for a second. Bannon’s evil, not stupid.
He’s either trying to save his own skin, or simply trying to throw opponents off his scent (which I can only imagine is both pungent and rancid).
Anyway, if it’s true that Trump has soured on Bannon, Trump might be tempted to sack him right now, conveniently killing two birds with one stone: 1, he gets rid of someone he no longer likes or trusts, and 2, he (Trump) can appear to be distancing himself from the alt-right, even though he’s not. So Bannon, by dissing ethno-nationalists, might be seeking to make himself appear to be less of a racist and hence a less juicy target for Trump’s Mighty Firing Fist.
Or, otoh, this whole thing could have been plotted out by the two of them, with Bannon’s interview intended–again–to confuse the situation by appearing to uncouple him from a significant portion of the alt-right, with the intention of throwing the anti-fascists and the media off stride. Simple but still thoroughly dishonest.
In any case, I don’t for one second think Bannon slipped up. His predatory skills are far too good for that.