If the joke was from, say a Middle Eastern, Indian, African or anyone other than those countries with rednecks all over, Aussies would have laughed at it, even if Aussies pride themselves as a tolerant and multi-cultural society rightly or wrongly. But coming from an American, notorious for their own redneck species, does not go down well. It is even worse when he says Aussies are English rednecks...who are also notorious for their racism against Pakistanis etc.
My personal opinion and experience is that Aussies are more laid back and friendlier than Europeans and Americans. However, because of their friendliness, they are not really politically correct all the time. They are a bit FOZOOL in a way as compared to, say Californians. A Californian is warm and friendly but avoid trouble questions whereas an Aussie, and worse the Kiwis (New Zealanders), will initiate talks about things you hate most to be asked, e.g. Ayatollahs, treatment of women etc. Correct me if I am wrong but most Californians do not ask you if you do not talk about it yourself. The other thing pisses Iranian off here is their lack of understanding about the Arab/Iranian difference. I do not even think it is an issue but I know people get really pissed off about it. That, in America is the same. But in Europe they know we are really different but they say...what the heck..the same sh!t!