Having watched all of quali and the race now in more detail, it's clear that Nico was working the steering wheel well in advance of when he needed to make that corner. It would be interesting to see a side-by-side comparison of his pole lap going into that corner and the crash-lap at the same place - but having seen them both I'm more convinced he did it on purpose. Stoopid Sky for not doing that comparison.
In fact I think he got his crash a bit wrong, and didn't quite lose it enough to spin. Once he got into the escape road he could have quite easily driven right to the end of it, but no, he thought for a bit then reversed! That adds fuel to the fire surely.