From what I can tell its actually both a fork and a premine...

However the details have since been removed from their site, originally they explained it.
Here is how I understand it. After the fork, everyone who holds BTC private keys gets their 1:1 BitcoinGPU (BTG). They are ALSO doing an ICO where they advance the blockchain manually (not sure how) 16,000 blocks, and keep the block rewards of 12.5 BTG/block = 200,000BTG.
They will be selling the ICO at 1:10 BTC:BTG.
Can anyone confirm or deny this?
Sounds like huge shit show to me. but you never know.
I don't think that will happen there is only supposed to be 1 week from fork to launch so there may be a few premine blocks but not many