While I'm sure Red Roo can't speak for or represent other airlines/lounges, OW or otherwise, there's enough evidence on this and other similar forums to demonstrate these instances happen time and time again, including at Qantas lounges of all levels. While I'm sure the staff at the entrances have to deal with numerous attempts of people trying to gain access where they do not have any rights, it is irksome that it is incumbent on the passenger to have to prove to the staff that access is available (yes, CNS QP staff, I'm looking at you too). I mean, in simplistic generalisation, what else do the staff at the entrance counters have to do or know other than the access rules?
If this was me in this situation, I would be extremely angry and entirely disappointed. I am often looking to extend the privileges and enjoyment I experience as a loyal customer of Qantas/OneWorld with my family members, including my parents, and I know if I was in a similar situation, I would be absolutely gutted if my parents had been denied access to the First Lounge due to the absolute failure and incompetence of a Qantas staff member. While each of us have different travel patterns, an international trip is an exception for me, and the visit to the First Lounge would have been a highlight of the trip. In the hum-drum of performing their routine day-to-day job, this is an aspect that the staff seem to often forget: access to a lounge is part of the travel experience, and not taken for granted. It may seem a simple task for them to say 'no' in ignorance, and to stick to their guns, but do they actually appreciate the full ramifications of what they are denying to the (fully-eligible) passenger?
Additionally, if a staff member in my company represented my company in the manner in which this staff member is reported to have represented Qantas, they would no longer be representing my company.