The 70% target is the point at which states have agreed to stop locking out each other, it has zero to do with when states ease restrictions within their own state.
NSW has not agreed to keep greater Sydney in the current strict lock down until we reach 70% vaccination, no state has. When cases are manageable, localised restictions will lift. Other states can choose to keep NSW locked out, but Gladys has stated our restrictions will lift over time (not a big bang) and we can expect more freedoms than we currently have before the 70% target is reached if case numbers fall.
It was reported on news.com(.au) this morning - the NSW Premier stated that 70% would end the lockdown in Sydney. It seems the article has now been updated and mentions 80%. I think the point was that the 70% would allow NSW to end their lockdown much sooner than if they tried to control it by other means.