My understanding, from how people use it here is that irony is a situation which is a contrast between the expected/intended and actual outcome.
It's ironic when a fire station burns down
This definition is truly upsetting: https://www.merriam-webster.com/dictionary/irony
Americans, no. Bad Americans.
This definition is correct (until we come up with a good substitute, FFS America): https://en.wikipedia.org/wiki/Irony
Glad Wikipedia agrees with me on this one haha We'll at least the introductory definition.
Edit: to answer your question. I dunno. I just think this form of "ironic" just didn't take off in Australia.
Mostly because we already have words for what Americans use it for. And don't have words to replace irony.
¯\_(ツ)_/¯
I don't think I've ever heard sarcasm used when irony is appropriate. Because "ironically" seems to be taking over (for Americans, not in Australia)
"That's so sarcastic" referring to irony isn't a thing. Or at least, I've neve heard it.
"the use of words that are the opposite of what you mean" bad Cambridge, bad! That's sarcasm.
Could be my cultural context, and my bias because I constantly hear Americans misusing 'ironic'.
Don't use it differently without providing a replacement please and thank you!
Wikipedia gets it right: https://en.wikipedia.org/wiki/Irony "Irony is a juxtaposition of what, on the surface, appears to be the case with what is actually or expected to be the case"