All posts returned when author of 0 is queried

I have a small problem when attempting to query some posts by author.
I have events and registrations. Currently I have 4 registrations, all created by User2 with the wp-admin showing that correctly. If I run the following code with a user logged on it works. User2 shows all and User1 shows none.
However, if no-one is logged on it returns all of the registrations. The user_id is being shown as 0 so it shouldn’t find any of the registrations but it finds all of them, those for user 1 and those for user 2. Is there anyway I could stop this without having to check is_user_logged_in() each time.

Thanks