Yes they could, but without knowing what those keys there really is no way of saying who created them.
If my memory serves me well, when you first install a third party antivirus Windows does create some HKey Local Machine entries relating to that AV. I guess there is also the relationship that it and not Defender is the default AV.
When you uninstall Avast those registry entries are still controlled by the OS and in due course the OS would remove them.
This relates to the Avast Remediation exe file, I really don't know who gives these names, but I believe it is related to checking your installation for errors, etc (to presumably remedy the problem or report it). Because of the nature of this tool I guess it could be stand alone or it couldn't check the correct working of the Avast installation.
I have an entry for this in my Task Manager and that is where the AvastWscReporter service enters the picture.
If you have uninstalled avast, then this Avast Remediation exe entry wouldn't be in the Task manager ?
If not any registry entry for the AvastWscReporter service would be redundant.