You're thinking of gvisor. But no, the "gen2" runtime is a microvm ala firecracker and performs a lot better as a result.
And it looks like Cloud Run can do something Lambda can't: https://cloud.google.com/run/docs/create-jobs . "Unlike a Cloud Run service, which listens for and serves requests, a Cloud Run job only runs its tasks and exits when finished. A job does not listen for or serve requests."
Google built crosvm which was the initial inspiration for firecracker, but Cloud Run runs on top of Borg (this fact is publicly documented). Borg is closed source, so it's possible the specific hypervisor they're using is as well.