In fact Mandel was not able to calculate the odds of multiple winners. With publicity about an outsized jackpot, the general public is also expected to buy tickets in larger numbers, making it hard to estimate the expected winnings.
For that reason, I would not consider this to be gaming, or cheating the lottery. There was no guaranteed profit, and a moderate chance of large losses. So he took a big gamble, and was lucky to be the only winner in the end.
An interesting question is whether lotteries should publish the number of tickets sold when it implies expected winnings for every single ticket sold (as was the case in Mandel's lottery). On the one hand that should sell more tickets, but on the other hand it will deter some people from buying once the numbers stop being published...