Another reason to suspect that the underwater video has to do with Sony's Android flagship model is because we have already shown you video of the phone shooting frames underwater in a pool. The Sony Xperia Z is an IP57 certified device. That means the phone can live after being submerged in water at a depth between 15cm and 1 meter for as long as 30 minutes. It also means that when it comes to dust, the Xperia Z offers "limited dust ingress protection".
source: T-Mobile via AndroidAuthority