So what do you call it when the media is spruking a "sure thing" Labor win on a daily basis in the lead up to the election, and citing these opinion polls, and then the actual voting goes the other way? Other than faulted methodology.
https://en.wikipedia.org/wiki/Opinion_polling_for_the_2019_Australian_federal_election
You're kind of just repeating yourself here. Polling, if done correctly, shows what a representative sample of what the population is thinking. It is specifically designed to remove the 'noise' and discussion from the equation to give a simple quantitative outcome. Every person involved in polling has the same amount of say as each other, it's impossible to have a 'silent' anything in polling, unless people are deliberately misleading in their answers or the polls are badly designed. The media reporting on the polls and what they suggest, if done objectively, is nothing more than a communication of a quantitative measure.
If you're talking about opinion pieces and editorials, sure, that's part of the discussion where you can talk about who is making the most noise. But that's not what it seems you're referring to, given your citing of polling.
There's a very clear history of the term, which was coined by Nixon when referring to anti-war protesters, which was used by Howard when referring to the moves to have him voted out, etc. This election flipped expectations, based on polling, no doubt about that. However, to say that the Liberal base was silent in this election campaign is pretty off the mark, in my opinion.