This is more of an ANSTO PR piece to promote a new piece of kit [1] based on a recent paper [2].
I'm guessing they loved the opportunity to field test this in a sea of global public interest.
What they're not actually saying is that the source in question could have just as easily been found using 1990s technology in a low flying aircraft at 70m/sec ( ~250 km/hr ) - once you get the target peaks (which were bright against the background) in a 70m square it's a simple matter to wave handheld detectors about to zero in on the capsule by the road.
Also of note "How to find .." is somewhat misleading is there is great deal of gloss here but relatively little substance.
[1] https://www.ansto.gov.au/products/detection-and-imaging-cori...
[2] https://iopscience.iop.org/article/10.1088/1748-0221/15/04/P...