The clue is in the title there - it says nothing about the amount of corruption, only the perception of it. People notice the low-level corruption of petty officials asking for a few bucks, but they're largely blind to high-level corruption that takes place behind closed doors.
The same John Barilaro who resigned as deputy premiere of NSW because it was getting very hard to cover up all the corrupt schemes he was involved in. The same fella who created a special job paying six figures and then handed it to himself, while still in office: https://en.wikipedia.org/wiki/John_Barilaro#Investment_NSW_a...
Of course, there's no corruption here - hence our infallible public rightly perceiving none of it! (/s)
Perception, yes. Being on top of the CPI tells nothing about how well the country is doing. It merely highlights how bad the situation is even for the runner-up.