I got a paywall, so here's another article.

Short version. Chef was on an employment visa, and had allegedly refused to make it on several cases. Owner was annoyed but sympathetic as he doesn't really like it either, but they had a large group (estimated AU$15k) event, and the paying customer had requested ham and pineapple pizza. Chef refused. Owner fired him but waited as long as possible to inform Immigration, hoping the final visa would come through. Chef claimed it was retaliation "partly" over a broken hand, but tribunal said he'd waited too long to bring it up. Eventually, restaurant closed but chef found other work and is still in the country.

Another article says there were other things, "including allegations relating to foul language, communication issues and escalating frustration at work." Sounds like the chef was a bit of a cliched chef personality, to be honest, and maybe not talented enough to pull that act off. If the restaurant is also not doing well, then I could see the "Italians must not put pineapple on pizza" thing being a lot less cute if it messed up a big event.