As I mentioned, the system metrics come from reading procfs. I see that you get the host metrics reading procfs from inside a container (checked on a Proxmox server), and it is not the case for qemu/kvm VMs. I think this is by design (shared kernel) and not a bug. Netdata reports whatever kernel reports (procfs).
Thanks, @philip. Netdata gathers containers/VMs metrics reading the /sys/fs/cgroup/* directory (see cgroups.plugin). It is easy to add oom_kills metric/chart, but it is not really useful from my experience - if OOM killer kills the main process (which is likely) in the container that counter doesn’t get incremented.