The analysis seems mostly[1] solid but the conclusions are all wrong. The steam machine was sold out and wait-listed. Value doesn't charge until you are removed from the wait-list so these numbers reflect the number of manufactured units per week (e.g. manufacturing capacity and/or distribution strategy) of the steam machine and not demand. This is only a minimum demand. To get the demand you would need to derive info about the length of the waiting list.

[1] The unit mix would be what valve picked as the initial mix and not necessarily the market average. Also, the sales numbers would include the steam controller if you selected that option but I don't know if there is good data on whether any of the initial reservations had the steam controller.

I read the analysis and I don’t see anywhere that it claims to measure demand.

It seems pretty clear it’s about how many units Valve is selling (charging for, shipping) and explicitly not about reservations or demand.

Valve is being smart here. It is far better to be supply constrained at launch than to have enough capacity to meet initial demand (and then far too much capacity when demand slows over time).