Yes - different places, different rules. Over here, BA also provides lounge access for all short-haul business class pax, whether it's domestic or European. But then the entire model is different, as BA simply has no paid access scheme for its lounges at all.

Althought it's a bit late now, I still wonder what the lounge staff would have done if your parents had said that they were on an international QF trip, and that these were just the domestic sectors which they'd happened to have bought separately. While there are some dragons, I have had far more indulgences from QF lounge staff over the years.