Yes the website is definitely wrong, all previous release Topo Aust version 2 and Topo Aust & NZ versions 3 & 4 are 20m contour intervals.
Only the competing OzTopo map includes 10m contours as a separate image. The only other commercial offering for Garmin I'm aware of is TopoPlus Aust 5m contours only (no map) through local GPS retailer but as the DEM from which it's derived is very coarse it's full of artifacts.
Personally I prefer the 20m as good balance with less clutter for hilly area's. None of them are accurate, it's purely a visual thing.
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