His logic is sound:

Part of the reason standing desks seemed so unintuitive to me at first was because I associate standing with a kind of temporariness — you stand when you’re doing something like talking on a pay phone, or waiting for the ATM, not while you’re settling into a major task. But that sense of temporariness may be the genius of it, if it can help a person get down to work more assertively.

Put another way, sitting is a highly passive state, perfectly suited for self-entertainment or other effortless activities, and perhaps not so well suited for focused work. I suspect that standing makes a person less inclined to play and more inclined to work. I can easily spend four hours in a chair doing one hour of work and three hours of not-work. But there’s no way I’m going to spend four hours standing just to spend most of it dicking around.