From the link it says:
I: Not eligible – you have not satisfied additional selection criteria.
You are not eligible for an offer to this course as you do not meet the additional selection criteria. If you do not know what the additional selection
criteria are for this course, check the course description by using UAC’s course search.
In this case the additional selection criteria would have been a high enough interview score and a high enough umat score so that combined he would rank in the top X people applying when combined with his ATAR.
Congratulations to your son (you should get him to post and ask questions on here himself - he may find it useful!) for getting other offers, but unfortunately, at least, for this offer round, he did not score high enough to receive a UNSW place. He may very well be eligible for one in future rounds.
Bear in mind that other than for the purposes of determining your internship location, no one cares about where you did your degree nor do they care about the name of your medical degree just as long as it was done in Australia or NZ. He should be equally able to practice medicine in Australia if he were to go to UQ or JCU - except that he would likely be working in Queensland rather than NSW.