Second of all, I don't really understand why you think I'd be blown away by the notion that you can use Kubernetes to run a single container. You can also open a can with a nuclear warhead, does not mean it makes any sense.
In production systems, Kubernetes and its ecosystem are very useful for providing the kinds of things that are table stakes, like zero-downtime deployments, metric collection and monitoring, resource provisioning, load balancing, distributed CRON, etc. which absolutely doesn't come for free either in terms of complexity or resource utilization.
But if all you need to do is run one container on a Raspberry Pi and don't care about any of that stuff, then even something stripped down like k3s is simply not necessary. You can use it if you want to, but it's overkill, and you'll be spending memory and CPU cycles on shit you are basically not using. Literally anything can schedule a single pod on a single node. A systemd Podman unit will certainly work, for example, and it will involve significantly less YAML as a bonus.
I don't think the point I'm making is particularly nuanced here. It's basically YAGNI but for infrastructure.