Earlier quoted context omitted.
A disruptive innovation is an innovation that creates a new market. What market does the Chromebook create that a $200 netbook didn't already create?
These things are only obvious in retrospect. Why did the iPod create a new market when the Nomad MP3 Player already existed?
One could argue the Nomad's market was much smaller (most people who bought iPods had never heard of it), partly because of Apple's aggressive advertising... which certainly helps "create" a market.