The manufacturer's website also states the following:
The Xperia Z5 Compact is waterproof and dust-proof. So you don't have to worry if you get caught in the rain or want to rinse off dirt under the tap, as long as a few simple instructions are followed: All connections and covers must be tightly closed. One must not bring the unit into contact with sea water, salt water, chlorinated water or drinks and similar liquids. Misuse or improper use of the unit will invalidate the warranty. The unit is protected according to IP protection classes 65/68. For more information, visit
https://www.sonymobile.com/waterproof. Caution: The Xperia Z5 Compact has a USB port without a cover that can be used to connect and charge the smartphone. If the device has been in contact with water, the USB port must be completely dry before it can be charged.
I don't think Sony knows this very well and defines the whole thing as unclearly as possible, so that in the event of a warranty claim, the rights lie with Sony.