„Container“ is sort of synonymous with „OCI-compatible container“ these days, and OCI itself is basically a retcon standard for docker (runtime, images etc.). So from that perspective every „container system“ is necessarily „docker-like“ and that means Linux namespaces and cgroups.
Interesting. My experience w/ HP-UX was in the 90s, but this (Integrity Virtual Machines) was released in 2005. I might call out FreeBSD Jails (2000) or Solaris Zones (2005) as an earlier and a more significant case respectively. I appreciate the insight, though, never knew about HP-UX.
History is one thing, who-did-it-first is often just a way to make a point in faction debates. In the broader picture, it makes little difference IMHO.