I agree on what he said because even me I can sometimes wager a high amount using only a small capital but I think it doesn't happen at all times but most of the times I can only wager sufficient amounts because it will be a loss to the casino if they make their games easier for the players because you know, we can also get rewards through wagering and amount of it can base on how high or low we wager.
Whales have big budgets so it is more possible for them to wager that high even at all times because once they lose their deposits, they can always redeposit again and again till they hit their desired wager amounts.
Obviously it could be someone who wagered a lot by using a lot of money, that is of course the common conception and probability of that is much much higher. I just wanted to point out that it is not a "must", doesn't mean that it has to be a whale for someone to wager that much, obviously it is a lot more possible for someone to be a whale in order to wager that much but it could very well be someone with just a few bitcoins that did it as well, it is not impossible for that one to be the case.
I do agree that it is more likely for someone with 100 bitcoins to be able to wager this much, but it is also quite possible for someone to wager and win with 4-5 btc as well.