I believe that's an Intel project, not a Google project. I personally think it's more likely Cloud Run is on top of the same proprietary KVM-based code they use for their Compute Engine.

Possibly? I haven't found any public documentation that says specifically what hypervisor is used.

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.