I called P1 services and they said to me.no, he is allowed in and gave me the lounge number in Brisbane.
It sounds as if the local QF staff were very accommodating to the OP's son in the circumstances. Good on them!
That said, on the basis of the OP's information, it is disappointing that the P1 hotline would advise incorrect information that they could so easily verify.
It is no wonder that customers become confused when misinformed.