How do premined coins work? How does the concept of premining coins work?

For example, bitcoin gold is said to have 16,000 blocks premined. Well, at the current block reward of 12.5 bitcoins, 16000*12.5= 200,000 coins will premined for the developers which sounds sort of like a scam to me.

Anyways, how is this possible? Miners get rewarded for transactions they process. How do coins get premined on future blocks before being released?
Those are called "pump and dump" schemes. First you own a large amount of coins, then you make your coins public and try to convince everyone to use your coin, so its value will rise and you'll be rich.


  ... sort of like a scam to me


Well, a rumor that says Satoshi owns 1M Bitcoins (Source)


  ... how is this possible?


Bitcoin Gold will change the PoW to a GPU algorithm. Thus, the difficulty will start at "one" or so. Hence generating coins will be easy until the difficulty adjustment happens.


  How do coins get premined on future blocks before being released


Again, first they'll mine, then they'll make it public.