They're now reporting the true activity of the source is indeed 19 gigabecquerel.
"Chief Health Officer Andrew Robertson said the small silver cylinder was a 19-gigabecquerel caesium 137 ceramic source commonly used in radiation gauges.
“That may not mean a lot to people but probably more concerning is that it does emit a reasonable amount of radiation,” he said.
Dr Robertson said the unit emits about two millisieverts of radiation per hour, which is the equivalent of having 10 x-rays in an hour".
To compare, the maximum dose rate permitted for radiation classified workers in Australia is 20 millisieverts per year.
Outback hunt for lost radioactive capsule - Australian Associated Press (aap.com.au)