LXC containers can belong to root and be run as root, no problem.
You can even run unprivileged containers as root, but then the root user needs to have SUBUID and SUBGID ranges assigned. You can assign those with
usermod (or editing /etc/subuid and /etc/subgid by hand, if you’re so inclined).
If there are no SUBUID/SUBGID entries for root in those files, then containers created by root will be privileged. This works perfectly well, but it’s inherently less secure, since a process in the container that somehow manages to escape it, then runs as root on the host.
With an unprivileged container, such a process would have a very high UID on the host, which is unassigned there, so it effectively runs as user nobody on the host.