I wonder if they are counting Chromebooks which run a modified Linux. Those are starting to catch Mac https://www.theguardian.com/technology/2016/may/23/chromeboo...
But remember that Chromebooks are a US only story. There are very few of them outside the USA. One good year in the USA doesn't gain many percentage points in a worldwide stat.
Once in a while, in a blue moon, I see one single device at Saturn megastores in Germany. Usually it stays at the store with increasing "product of the week" discounts until someone finally takes it away.
In Portugal, Italy and Greece I am yet to bump into a store selling them.