The article quotes him saying more:

The five-minute piece is dedicated to the journalists of Gaza and was written for Gillham, according to D’Netto’s website. On Wednesday morning, Gillham’s team released the full transcript of what he said while introducing Witness.

“Over the last 10 months, Israel has killed more than one hundred Palestinian journalists,” Gillham told the crowd on Sunday.

“A number of these have been targeted assassinations of prominent journalists as they were travelling in marked press vehicles or wearing their press jackets. The killing of journalists is a war crime in international law, and it is done in an effort to prevent the documentation and broadcasting of war crimes to the world.

“In addition to the role of journalists who bear witness, the word Witness in Arabic is Shaheed, which also means Martyr.”

Nah it wouldn't be that, those sorts of land acknowledgements are very common in Melbourne, especially in the Arts, that would have been perceived as utterly uncontroversial by the MSO

He was cancelled for calling Aboriginal people victims of settler-colonialism in Australia

Extremely unlikely. Australia's colonial history and its impact on Indigenous Australians is a very common theme in modern Australian classical music and many concerts I have been to, including one just the other week, have conductors or soloists introduce the piece and specifically cite the context behind it. Unless the MSO is significantly different (which it doesn't appear to be, based on some quick searches of Indigenous-themed concerts) this is not the reason. It was his comments about Israel targeting and killing journalists (what you quoted is not the actual introduction he made at the concert) which led to the cancellation.