I can't explain that.  It's been a while, but when I removed Avast using the Control Panel when I last removed it I just got the standard, "Do you want to uninstall this program?," dialog.  There was nothing special about it.

The only other thing I can recommend, if Control Panel is not accessible for Avast removal, is to download and use the Avast Uninstaller Utility.
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Brian - Windows 10 Pro, 64-Bit, Version 1809, Build 17763  

Puritanism:  The haunting fear that someone, somewhere, may be happy.

        ~ H.L. Mencken