I wouldn't take Balaji serious, remember nearly a year ago he was supposedly the overnight coronavirus expert and "wins" arguments with journalists by pointing out how much money he makes: https://twitter.com/balajis/status/1252409386451922946?s=20
Explain? I'm aware that giving a host user permission to control Docker is equivalent to root, but that's no worse than wheel/sudo in most cases, and not a "sandbox" failure. So I assume you're thinking of container escape, which I was given to believe is actually hard these days?
Docker use shared resources like Kernel. Linux Kernel is big ugly C mess (Compared to includeOS) and probably one can find a good enough exploit for the kernel then escape the Docker.
That's and VM provides much better security. Well, VM escape exploits exists but they are at least much harder than say a Docker level escape.
He was referring to sandboxing in terms of not polluting the installed packages/libraries on the server and not from a security perspective. But even from a security perspective, there are solutions to this problem like running containers as an unprivileged user using podman.
