Go to multipools blocks found shows 20 to 49 and then the 1081 and so on so pretty sure that address where those 570 mill coins went is multipool. Doesn't show 1-19 but its the same address so doesn't look pre-mined to me.
There are two ways to premine.
1) premine
2) open a pool, the only pool, with the only compiled ready to mine wallet, wait 5 minutes with 1TH, solve 100 blocks, then call it a day.
Oh but #2 isn't a technical pre-mine. It is the obvious consequence. What's the difference?
It wasn't premined shows the users that found the block as well. Me being one of them early on.