Note that Cloud Run is not built on Kubernetes, but on Borg. It implements the Knative Serving API spec, mainly for portability reason with Knative and Kubernertes.
Source: I'm the Cloud Run PM and we have commmunicated about that publicly in the past.
Do you have any Google docs or blog posts that talk about this?
I always wondered why you need a Serverless VPC connector for "vanilla" Cloud Run (or you have to use Cloud Run on GKE) to access VPC resources, but I suppose this answers that question.
Source: I'm the Cloud Run PM and we have commmunicated about that publicly in the past.