No, I understand what you are saying about not requiring user accounts and the signups.
The code is designed to get the current user id if there is one from the form, otherwise it uses the current user id (which would be you, in this case). Some people like that feature, because if the admin is managing all the sign-ups, then they also have a nice list of signups on the front end main signup page that they can easily clear, if needed, as opposed to hunting through individual sheets in the back end to find the signup they need to clear.
Perhaps that can be another option/setting for a future update.