And passengers are the public.
Any select group of people are also part of 'the public.'
Police are also part of the public, but it doesn't mean you can go anywhere in a police station. Back areas of a police station are restricted to staff and authorised visitors, including of course people making reports - and of course detainees. Back areas of an airport are restricted to ASIC cardholders on official duties, and passengers with identification. Neither are public areas even though people aside from employees are there.
I can only suggest that the next time you are in that area you water one of the plants with your in built "hose". I'm pretty sure that the police will charge you with urinating in a public place.
Good luck with that analogy next time you're in court.