Coinmarketcap is a decent site... you just have completely ignore the market cap figure. Not because of the site but because that is a completely meaningless number in crypto. Sort coins by liquidity (24h volume) to see what's what. Although it would be nice if we had liquidity figures for longer periods of time.
The guys who made that coin premined it then had the site coinmarketcap promise (in advance / before launch)
that they would add the coin with premined coins considered as part of the "Cap"
That is how it should work; all coins premined/mined/ico/swapped/whatever should be part of the cap, because they are available, exchangeable coins even if a dev swears he won't touch the premine.