TFA mentions the truck was passing by at 70km/h, which is surprisingly quick.

You'd think that was quick, ... but generally this kind of thing would be done from a crop duster airframe flying at an industry standard 70m/sec (252 km/hr).

I'm guessing the local Perth geophysical survey companies that routinely flay magnetics and radiometrics were all fully engaged flying pre booked contract work .. so they dragged in a couple of white transit vans and fitted them out to get the job done.

Switzerland uses Superpumas flying 90m over areas to measure radiation on the ground[1] . In around 3 hours they can measure 100 square kilometers.

[1] https://www.tagblatt.ch/ostschweiz/im-tiefflug-ueber-der-sta... (german)

Sounds like the sort of complex setup developed prior for other more exotic use cases...

Complex?

Seems straightforward enough in the geophysical instrumentation domain.

Exotic? Radiometric mapping has been around for 50+ years - Australia has mapped the entire country (size of mainland contiguous USofA) from aircraft with ~200m line spacing in that time (along with surveying other countries, Mali, Fiji, India|Pakistan border, elsewhere), Russia, South Africa, Finland, USofA also have radiometric survey teams.

It's handy for finding drums of radioactive waste in a Finnish forrest near the Russia border, for example, which was an actual contest | exercise some years ago.

Which military based in Australia do you think helped by supplying this?

Australian civilian radiation services with backing of AGSO (Australian Geological Survey Organisation) are easily able to handle this all within Australia w/out reaching out to the Indians, Pakistani's, Iranians, Russians, South Africans, or other international nuclear agencies.