Basic numbers say that this can’t be true.

NZ net migrant arrivals is 151,000 give or take (https://www.stats.govt.nz/information-releases/international-migration-january-2019)

If as the post claims, 70% of these people then went on to SCV in Australia then you’d need roughly 105,000 kiwis going onto the SCV a year.

2016 Aussie census says there’s approximately 650-700,000 kiwis in Australia (let’s ignore the by ancestory and by birth thing for a moment)

Fundamentally even if every kiwi in Australia wasn’t born in NZ, this still isn’t possible. Even if a huge chunk went there and then came back this still seems massively unlikely.

Plus fundamentally I don’t know where some of these numbers are coming from because I’ve never seen anything published on what nation SCV recipients have originally come from.