Unless the auto-update terms in Windows Update expressly state that using it means you agree to any future, unknown terms that may apply to those updates, then

Unless the auto-update terms in Windows Update expressly state that using it means you agree to any future, unknown terms that may apply to those updates, then agreeing to automatic updates would not be sufficient. That is, unless the terms for Windows 10 are exactly the same as the version from which you are upgrading. That hardly seems likely, given that it is free and comes with new features, such as advertising, etc.