I do not know for sure. My believe is, that kids at that age sometimes simply do not know what they are able to do or not. They watch others, as they climb down the ladder and they just imitate them, somehow expecting the same outcome. This boy for sure was not able to swim, but he probably didn't know it. He perfectly copied the behaviour of other people entering the pool and then was maybe completely stunned that he did not float, but sink, I guess. He was in a age where most kids in Germany are confident swimmers and like to dive as well. It was not obvious to us that something was wrong, because his behaviour was so confident. He did not hesitate to climb down, and there were no sudden unexpected movements when he was under. I mean, we did not watch him specifically and guessed whether he was in trouble or not - he was just behaving just like any other boy. And you do not press the stop watch when a kid enters a pool. It just took some time until our subconscious minds shouted "something is wrong - it is too long!".

He entered the pool, face to the stairs, hands on the rails, continued to climb until the ladder ended (with his head already under water), released the rails, and sank, vertically, until the bottom. It was not a very deep pool, maybe 1.70m or so. He seemed to stand there, as if trying to see how long he could keep his breath. And when he shifted out of the upright position it became obvious that he was in trouble. A man standing next grabbed him, pulled him up, saw the boy was unconscious, started to shout for help and within seconds the boy was out of the pool and the lifeguards took over.