They save the world on multiple occasions, they're entitled to using unconventional means of package transportation.

Fortunately for Noctis, Kuai only boasts when it comes to battle, and this challenge doesn't count, "Nearly there."

Maybe he got cocky because his next one nearly makes it to shore before sliding off and teetering on the edge for a second before crashing into the water with a splash. At least it's floating for easy recovery later.