The installer specifically is looking at HKLMSoftwarePoliciesMicrosoftWindowsWindowsUpdateAU. It requires that the value for “NoAutoUpdate” is set to a 1. If you look in your registry and that value is not set, then you may think that you disabled windows updates, but you actually have not. That setting is the only one that will absolutely prevent any OS updates from taking place in Windows 10.
(For Windows 7, simply set the Windows Updates pull-down to Never.)