It's OpenStack on Kubernetes because we deploy the OpenStack components on a baremetal Kubernetes cluster (with actual payloads running in VMware), and it's Kubernetes on OpenStack because we have an addon service that allows customers to spin up Kubernetes on the VMware VMs created by OpenStack. We also dogfood this because the baremetal Kubernetes cluster is not large enough to hold all our internal services.
The parallels between the two are startling, i.e. at the beginning of OpenStack vendors tried to differentiate themselves by solving distribution/installation and plug-ins/integrations. How many K8s distros/installers are out there right now? Countless... [0] provides an interesting angle to the discussion that vendors trying their best to differentiate themselves is what ultimately led to the demise of OpenStack. I'm so far optimistic the same won't happen to K8s. Google is investing into K8s as a vehicle to gravitate workloads to GCP, but in order to do so it has to maintain some level of compatibility to other cloud vendors.