The title is ironic because winning a lottery usually means you get a prize, when in this case it means you die.
Irony is when the opposite of what is expected happens. In our culture, a lottery is usually a good thing. The winner of a lottery gets some kind of prize, such as money. We want to win lotteries. They will make our lives better.
The lottery in this village is not quite the same. Everyone shows up for the lottery, but no one really wants to be there. The first hint that something is wrong is that no one wants to go near the stool.
The villagers kept their distance, leaving a space between themselves and the stool, and … there was a hesitation before two men…came forward.
In this case, no one really wants to be part of the lottery. Yet tradition dictates they do it, and tradition is so strong that they dare not change it. The winner of the lottery is stoned to death, which is the opposite of winning a prize that makes your life better.