I see this is a no blocks extension. Does the developer simply drag the extension onto the designer window? Does this then generate the popup when you try to uninstall the app ? You should explain how it works.
Tested on simple app. Get a popup but no information about any app data (there probably wasn't any), but perhaps it should say that - e.g. "There is no app data to keep" ?
I observe that this extension is no blocks. Is the extension just dragged onto the designer window by the developer? When you try to uninstall the app, does this cause the popup to appear? You should describe how it operates.
Regards picsapkstudio