I'm not certain of the admissions standard for that particular event, but the description says they "welcome those at all levels of engagement" so my guess is that the admissions process is for screening purposes.  Eli mentioned in his reply to Scott that using an admissions process lets us try to screen out applicants who have caused problems at past events or who seem likely to cause problems. I'd have to check with our Community Events team to be sure that's the reason here.