If you don't (or didn't) use the Curse client (now the Twitch client) to uninstall the addon, you leave .lua and (occasionaly) .lua.bak files behind in the WTF folder. Perhaps that's what the op means.
(specifically in the SavedVariables folder, or the character SavedVariables folder)
It should be noted here that I have absolutely no idea about what Minion does or doesn't leave behind.