A wins a plurality of first preference votes. Otherwise, voters are split between B and C. We assume that if a candidate places C as their first preference, they will place B as their second preference, and vice-versa.
In this scenario, whoever gets more first preference votes out of B and C will win the election since the other will place third and get knocked out of the race, so anybody who placed A as their first preference didn't get to express whether they'd prefer B or C.
If it wasn't obvious,
A: LNP
B/C: Labor/Greens
https://www.abc.net.au/news/elections/federal/2022/guide/bri...
The point is that A voters arguably should have voted such that they could influence which of these two candidates won. This would require 'lying' about which candidate is their favourite; i.e. strategic voting
Generally if you put someone above your ‘2 party preferred’ candidate either your vote flows down or it was irrelevant.
Was it razor thin on first preference then the bottom 2 or 3 crackpots sealing the deal? This is the only way I can think of that’wasted vote’ happening.