He doesn’t actually do the calculation required to give an estimate of what that number is.

Going on the stats in the article:

• assuming that Wukong has just surpassed the revenue of Steam Deck in the chart so we can treat their revenues as equal
• assuming Wukong price is $49.99 and average Steam Deck price is $500
• using the stat that 14m copies of Wukong sold on Steam so far

that would imply ~1.4m Steam Decks sold

The article does go on to say:

Keep in mind that by November last year, Valve said the Steam Deck had already sold “multiple millions”.

So really this (very rough estimate) is telling us nothing that we didn’t know already. The top seller charts are showing exactly what we would have expected to see.