That should have been removed using the clean tool.
In a perfect world that may be true; however, the Avast clean uninstaller does leaves some elements behind. I guess that’s why RejZjor created his own version to do a more thorough cleaning.
Any piece left over memory resident is a problem, when your using the clean tool, to diagnose an issue.
I disagree with your assumption because many uninstallers typically leave elements behind that lie dormant because they are never referenced again by the OS.