It's open source (https://github.com/cq2-co/cq2) and not part of Salesforce, both appealling features. But deeper than that I have no experience of Quip (and precious little of CQ2 beyond the blog post) so can't comment reliably.

How is Quip different from Google Docs? Neither are discussion tools. (I use Quip a lot)

Quip has almost exactly the same feature set as google docs — which part of quip were you referring to?