How much of this is regular people just not buying new computers anymore?
A lot of households that used to have had a laptop for each person have replaced those devices with phones and tablets. They weren't using Linux, so by removing them Linux market share would go up even if it hasn't actually grown.
I think the argument is that as less people have desktops and laptops, the only people left will be more technical (otherwise they'd just use a phone or tablet). The more technical people are also likely to use Linux. So as non-technical people move to tablets and phones, technical people make up a larger share of laptop/desktop users.