He was asking why Istio was not included as part of Kubernetes itself despite both projects originating at Google. I was implying that there must be some reason as Istio is not in the CNCF while Linkerd (arguably an Istio competitor) and Kubernetes are. To further that idea, it seems that Google wants to maintain direct control over Istio itself, rather than put it into an organization with multiple sources of institutional governance (Amazon, Huawei, Samsung, Microsoft, Oracle, etc.). If Istio or any other service mesh had been incorporated directly into Kubernetes by Google, they would have lost some control over it.

(There are also obvious technical reasons for decoupling something like this from Kubernetes, mostly the opinionated nature of forcing a service mesh over other potential solutions).