Apple never said any iPhone was waterproof. Here is what they actually said in the specs→https://www.apple.com/shop/buy-iphone/iphone-11 (scroll to the bottom)
iPhone 11 is splash, water and dust resistant and was tested under controlled laboratory conditions with a rating of IP68 under IEC standard 60529 (maximum depth of 2 meters up to 30 minutes). Splash, water and dust resistance are not permanent conditions and resistance might decrease as a result of normal wear. Do not attempt to charge a wet iPhone; refer to the user guide for cleaning and drying instructions. Liquid damage not covered under warranty.