This is the format collision discussion that has no solution so far. A tablet that runs windows is counted as Windows. A laptop that runs android does not. Neither does an android cellphone. It all boils down to web browser user agent fuckery. This is why steam’s numbers are more reliable than other sources, they’re direct hardware surveys.
But the point is that a steam deck is not (but in a way it is basically just) a PC. There are tablets than run desktop interfaces and now there are laptops that can be used as tablet. Eventually the artificial mobile vs. PC/desktop/laptop schism will stop making sense.