But an analysis by BloombergNEF has found electrolysers used in China could already be as little as a fifth of the cost estimated in a CSIRO roadmap released in 2018, which has been used as the basis for government estimates.

The Bloomberg NEF report referenced says no such thing. What it says is that:

.. the delivered cost of renewable hydrogen in China, India and Western Europe could fall to around $2/kg ($15/MMBtu) in 2030 and $1/kg ($7.4/MMBtu) in 2050.

That's speculation about what could be achieved if policies were adopted to subsidize production of green hydrogen and create a sufficient market to drive cost reductions.

That would be similar to what happened with wind turbines solar PV panels after Germany chose to go all in with high feed-in tariffs and subsidies at the opening of the energiewende.

Maybe there's some other report that has found that "electrolysers used in China could already be as little as a fifth of the cost estimated in a CSIRO roadmap". I haven't located it yet, and I'm inclined to doubt the supposed finding.