Discovering

[Jolt]

If by 'pretty much proven', you mean 'there is vague evidence, a significant part of which is based on native paintings of what might be Portuguese ships.'
And given some of the things painted on rocks by Australian natives, its hardly surprising that something which looks like a European ship would appear.

Regardless, the first CONFIRMED and undisputed exploration of Australia was made by the Dutch.

As to the rest, Magellan missed Australia by quite a ways. He did manage to circumnavigate the world, but I'm fairly sure it had been confirmed some time ago that the world was round (even in Europe), and the 'flat-earth' theory was generally confined to more rural areas.

By pretty much proven, I mean "significant evidence encountered" in the Atlas I mentioned, where the coast is charted. Native paintings are just a minor detail which have no relation with the Atlas (Though, it may be further proof, but as you said, it isn't a certainty.) This is so, and in such a way that recent Australian school books mention (As far as I've been told) that the Portuguese were indeed the discoverers of the island.

"Confirmed" is rather impossible. Unless someone had passed through the Pacific before Magellan. "Most probable" is probably the correct term. Anyhow, the rendez-vous theory is just my wishful thinking and comparing dates. But missing Australia by far, since that island wasn't even charted, and in the times we speak about doesn't seem to unlikely even if they were supposed to meet.