Indeed, this is kind of like the Sesame Street game of "Which thing doesn't belong?" And you're right to say it's the swimming pool that doesn't belong, because the swimming pool is the only thing on this slide that's actually very dangerous.
C'est un peu comme ce jeu de "Rue Sésame", "Cherchez l'intrus". Et ici, l'intrus est la piscine, car une piscine est la seule chose sur cette image qui est vraiment très dangereuse.