Apple could probably run a Mac vs PC billboard on this tweet alone.
Which means pretending that every single "unknown" desktop, which is a larger percentage than the Linux desktops, are Linux.
And also by considering ChromeBooks, which also have a larger percentage than Linux, are Linux.
What may make this happen is political risk. The rest of the world outside the US doesn't like the excessive dependency of Microsoft systems on servers in the US, especially when that may mean snooping or disconnection. This used to be just a theoretical objection, but under the Trump administration it's a practical one.