Yes. Traefik Docker Configuration Discovery finds the other Docker services/containers, that run within the same LXC. That’s expected.
What you could do is to run a second Traefik in your second LXC, forward all unknown requests from first Traefik to second. You just* need to make the second Traefik reachable from within first LCX, but at least not all services. It’s kind of hacky, there was a recent discussion with 2 configurations.
* Well, that "just" might be a bit misleading, as ChatGPT has a long 5 step process to enable this. Note that ChatGPT is sometimes wrong.
Maybe Proxmox has a simple switch to forward an external LXC port to the inside.