First, it's important to keep in mind that there are different forms of radiation: ionizing[1] which is dangerous and non-ionizing which is not typically dangerous[2]. Furthermore, ionizing radiation consists of three types, alpha, beta and gamma which have different properties and thus dangerous in different ways and amounts.
The source in question contained cesium-137, which decays almost entirely (95%) by emitting beta particles. The beta particles are stopped by about 1 meter of air[3], but can do significant damage to living cells if nearby.
Thus, trying to detect it is a bit like trying to see a bright flashlight in a fog. Even though it's bright you won't see it until you're really close.
[1]: https://en.wikipedia.org/wiki/Ionizing_radiation
How can it be so deadly/radioactive, yet so hard to detect?
Further, asking questions is indeed the point of these discussions. Re-reading the standards I see no prohibition.
And reading that reference article, the loss it cites was 19Tb (19 trillion bequerels). This lost capsule in Australia contains less than 100. So around what? 10 billion times less dangerous?
Thanks for the reference material, now I'm more sure than ever that this article is some kind of clickbait about a fairly miniscule risk being trumpeted as a national incident.