This is a corner crop of a photo shot at ISO 6400 and pushed by more than 2 stops in post. What I'm curious about is that thin line across the frame - it has appeared in one other high ISO photo, and I'm curious as to whether this sort of thing is a "normal" artifact for high ISO shooting... I'm not able to reproduce it on command, and again, this photo was pushed in post (it's also maxed on Clarity in ACR to really bring it out).
I've seen this with many but not all cameras when high ISO shots are pushed. I don't know the explanation for this specific type of banding, but you can rest assured that it is not a defect. My Leica M gives me this kind of banding with much less pushing necessary.