I came across this article http://www.networkworld.com/article/3100383/cloud-computing/the-worlds-of-openstack-and-containers-are-colliding.html. It talks about openstack running atop kubernetes. What does that actually mean? Going by what they do, openstack is more lower level (IAAS) compared to kubernetes (between IAAS and PAAS), as per my understanding.
There are many ways containers and OpenStack are being mixed. The article you quoted refers to a new-ish approach of running OpenStack servers inside containers. The advantage is for maintainability and scalability. Basically, kubernetes is in charge of orchestrating the various pieces that make an OpenStack service, instead of the more general approach of installing OpenStack services on bare metal or VM (see TripleO).