How much did the player bet?
I think there is nothing to laugh about on the post of @OP. This is a kind of marketing strategy of enticing readers to try their platform. Even other reputable casino do this kind of marketing scheme. They regularly announce players that just got a big win on their platform and it is also obvious that the casino is able to process this kind of winnings if it is trully won by a player since they publish it publicly..
I think you are right, it is legitimate for the business to announce the big wins of the players, although I think it would be better if it is the player himself who does it, but I understand that it is funny for him, because those big wins attract those who are not aware of the mathematics of gambling. Big wins are improbable, and the bigger the win the more mathematically improbable, but at the same time it is what attracts people the most. EuroMillions jackpots with 100 million euros attract a lot of bets, even though the probability of winning it is approximately 0.