I installed fiddler for redirecting ports of a database. Although later I found another solution, and thus I uninstalled it. On uninstalling, strangely on company vpn all external websites stopped working. And I could only access company websites. On spending some hours, I realized that my LAN setting was reset by Fiddler somehow. On checking, Detect settings automatically in Internet Options, everything started working again.
I confirm that since Eric left the project no code has been added to the installer that will change the proxy settings. Is it possible that FIddler crashed the last time you ran it before uninstalling it?
FWIW, I'm not aware of any code in Fiddler's uninstaller that would touch your proxy settings. Fiddler itself only touches them while it's running.