You're right in that you probably didn't have to bother non-ticketed event in public space. What I have often done, if in doubt, is to ask for credentials with the added note that if the event organizer did NOT issue credentials (highly likely) to reply to me with an email stating that they do not issue credentials. I then forward this response to SS. They in turn tell me I am pre-approved for credentials and to give the reviewer a case number.
A real PITA, wouldn't you say?