https://7news.com.au/news/aviation/j...-fire-c-749139
> Flight JQ660 departed Sydney just before 10.30am and was almost two hours into its journey when an indicator light suggested there was an “incident” in the cargo hold, a Jetstar spokesman said
He said early reports that a fire was detected in the cargo hold were incorrect
“(The flight) was diverted to Mildura as a precaution,” he said.
So yeah looks like not a fire. Detector or instrumentation problem then.