Schools are probably the biggest buyer of Chromebooks... especially the cheapest models. That certainly would skew the numbers. I am guessing the average Joe is not buying these devices for home use. In my experience, the cheapest Chromebooks (Samsung Series 3) are very poorly built, and there seems to be problems with WiFi connectivity. Maybe the Intel-powered Chromebooks are better, but I have not had experience with them. Anyway, Once schools (and others) use these devices for one or two years, it will be interesting to see if the sales numbers are sustainable and if the devices hold up to wear and tear, etc.
That said, I hope Apple has a plan in place to deal with schools buying Chromebooks in droves. I expect them to lose a lot of MacBook and even iPad sales next year. I hope they don't create a device that is pretty much dependent on the Internet. Maybe they could have an iPad type of device with a real keyboard that can run OS X. I know some are speculating that could be what Apple has in mind with the alleged iPad Pro. The price mould have to be in the $500 to $600 range, though, to compete with the low prices of Chromebooks.