They don't promise it's swim proof, but they promise it's water resistant up to 50 meters. He was in a shallow pool, so if water got inside, that's a failure on Apple's end.
Sorry, but that’s just not true. All the same, it’s worth checking with Apple directly. If the watch is under warranty I’d expect them to replace it. 50M is static pressure, it’s not for swimming down to 50M.
Have a read of Apple‘s content on their website:
Learn about water resistance on your Apple Watch and what to do if your device gets wet.
support.apple.com
Not once does the word “promise” appear. Instead:
…Your Apple Watch is water resistant, but not waterproof. For example, you can wear and use your Apple Watch during activities such as exercise (exposure to sweat is OK), walking in rain, and washing your hands
And
…Apple Watch Series 2 and later can be used for shallow-water activities like swimming in a pool or ocean, but you shouldn't use models other than Apple Watch Ultra for diving, water skiing, or other activities involving submersion below shallow depth or high-velocity water.
And
…Water resistance isn't a permanent condition and can diminish over time. Apple Watch can't be rechecked or resealed for water resistance.
