Aren't Chromebooks, tablets and smartphones thin clients to Google's mainframe, Facebook's mainframe, Apple's mainframe?
What processes the Siri commands? Who calculates the directions in your navigator?
So, I would argue, that for the period he is talking about the fat client and stand alone models were much more dominant than the thin client, in contrast to his expectation.
Or to use his reference point, nearly every university had its own computer in the 80s, rather than using a thin client to a host at MIT/Oxford/Harvard etc.
And in general, despite the cloud, I think fat clients are still dominant. I.e. look at gaming, the majority of processing is still done locally, despite MMOs and the internet.
EDIT: I think most people expected thin computing to dominate. But it turns out to be easier to manufacture and ship PCs around than data.
So, it wasn't because they thought the thin client approach was better, it was just the only realistic future they could see given the cost and size of computers at the time.