It's important to realize that Linux offers a-la-carte container features which evolved over time. Some of the features include chroot, process groups, user/group permissions, cgroups, network multiplexing (e.g. inetd, nat), namespaces (network, mount, pid, user, etc.) and unshare/setns, union file systems like unionfs/aufs/overlayfs, etc.. There are a lot of ways you can implement container orchestration systems on Linux.

And as noted, OpenVZ and Linux Vserver were earlier container subsystems for Linux.