ELI5: Why are Australians sometimes stereotyped as being laidback? What is it about Australian culture that presents as 'relaxed'?

I am 100% Australian and I've been told by countless tourists that Australians are super "chilled-out". Media portrays this sometimes too. I don't understand it? What sorts of things are other countries more strict about in comparison to Australia? Is it because we have more slang? Is it about like alcohol consumption or something (I didn't think Aussie's were big drinkers?).