I'm pretty sure that by Ghash, people mean Gigahash. 1 Gigahash = 1000 Megahashes, so the first one.
As binary doesn't apply, that's correct.
If it was memory/HDD storage, then it would be 1024.
Remember... there is a difference between a MB and a MiB. Memory is usual in XiB, while storage is normally in XB.