So what’s the stuff about waiting for this particular block and how is it utilised to decide the winner anyways?
That's how they designed the provably fair lottery.
For the lottery to be provably fair and the winning ticket to be chosen completely randomly, they use the hash of a block that will be mined in the future and is unknown when the tickets list is published as the client seed.
They could use the hash of 10, 15, 20 or any number of blocks in the future.