Shoutout to Michael Crosby, the person in this video, who was instrumental in getting Open Containers (https://opencontainers.org) to v1.0. He was a steady and calm force through a very rocky process.
And we can thank predecessor systems like BSD jails, Solaris zones, as well as Virtuozzo/openVZ and lxc as previous container systems on linux.
Docker's main improvements over lxc, as I understand it, were adding a layered, immutable image format (vs. repurposing existing VM image formats) and a "free" public image repository.
But the userspace implementation isn't exactly rocket science, which is why we periodically see HN posts of tiny systems that can run docker images.