It was a book I read when I was a kid, so I am assuming it was a book aimed at kids/young adults. A whole crew of aliens of different species meet an Earth kid. He befriends them. One of the aliens comes from a planet with dozens/hundreds of different sexes/genders.
At one point, the Earth kid is talking about a swamp:
Alien: "I live in/near a swamp on my home planet"
Kid: "Oh, do you come from a swamp planet?"
The alien points out that just because there is a swamp on his planet doesn't make it a swamp planet, there are dozens of biomes on his planet, just like Earth. Earth isn't just a swamp planet.