Is an unexpected occurance always ironic? Why or why not?

Answer 1

No.
To be ironic, there has to be some deeper level of unexpectedness.
Here's an example...
A very good tournament Scrabble player has a rack of DEEINTV. After studying the board for a while, he plays "DEVEIN" for 30 points, a pretty respectable score for a turn.
But the word he missed seeing, worth 70 points or so (that's counting the 50 pt bonus for using up all 7 tiles), was "EVIDENT". But obviously it wasn't evident to him, or else he'd have played it.
It's unexpected that he missed it... because he's a good player and doesn't normally miss seeing the right play... and it's ironic that the word he missed seeing describes something that is too obvious to be missed.
If his rack had been KUMQUAT or something, and he missed playing KUMQUAT, there'd be nothing ironic about it. What does a kumquat have to do with failing to see a Scrabble play? But it would still be unusual, because a good player would normally find "KUMQUAT".
Yes, I know, silly example, but first one that came to mind.