“Premining” is actually a made-up word, that we've defined it as a creation of some coins, before the cryptocurrency gets launched. Almost all cryptos are premined, even Bitcoin. Satoshi was mining for a month, before he/she announced it on bitcoin.org. I just wanted to point you that, let's move on.
You are gravely mistaken. Satoshi mined just one block for no more than six days. Furthermore that block cannot be spent, so in effect he premined 0 coins.