That is probably it. If you are concerned, you could fully delete that container and reboot, see if tunl0@none comes back.
I don't see any proof of a hack in the comments in this thread or in the diagnostics. Not saying it is impossible, just saying I don't see anything that would lead me to that conclusion.
Although I do see that your previous release was 6.11.5, which is about 1.5 years old, an eternity in Internet security terms. Even so, if the system is not exposed to the Internet the risks are minimal.
Unraid is different from most operating systems in that it is loaded fresh into RAM with every reboot. A hacker would need to take special steps for the hack to persist, and those should be visible in diagnostics. So in general once you reboot you are good. Although IF a hack did occur you should take steps to prevent it from happening again, I'd suggest reviewing our Security Best Practices:
https://unraid.net/blog/unraid-server-security-best-practices
and resetting your root password and user passwords to be safe.
(Note that if a Docker container was hacked, that would not be resolved by a reboot. To clean that up you would want to fully delete the affected container.)