I'm pretty sure many on the Windows design team would disagree with his characterization of the design goals.
I think the biggest wrong part is that the "consumption vs. productivity" thing was mostly about trying to reduce the scope of the scenarios the new UI would support in v1 (i.e., Windows 8.0) to make the project tractable (i.e., avoid another "Longhorn"). It wasn't really the intended end goal of the new UI in the long term - the idea was always that the scope of the new UI would gradually increase to support more scenarios, including productivity scenarios, until it eventually encompassed the overwhelming majority of usage for the overwhelming majority of users. We already saw some progress in that direction in Windows 8.1.
Also, "consumption vs. productivity" != "casual vs. power users". Not different groups of users, but different modes of operation, with many people doing both. The Windows group didn't really categorize people into casual and power users exactly, they had a concept of "enthusiasts vs. humans" which isn't quite the same thing and they didn't necessarily map it 1:1 to scenarios or features.