"If he wins seven golds and ties what I did, then it would be like I was the first man on the moon and he became the second. If he wins more than seven, then he becomes the first man on Mars. We'd both be unique"

Mark Spitz is describing his own success in the 1972 Olympics, where he won 7 gold medals. He is recommending that if another athlete were to match his task, it would be an amazing accomplishment, but not quite as excellent as his own. He is recommending that if somebody were to surpass his record and win more than 7 gold medals, then that professional athlete would be a lot more impressive, as if they had actually gone to Mars instead of the moon. He is highlighting the uniqueness of his own achievement, and suggesting that if someone were to exceed it, they would be much more special. He is also suggesting that both he and the professional athlete who exceeds him would be distinct in their own right.