A student who has just learnt to back-float and doggy paddle in the water (without proper strokes) are sometimes even more prone to danger than someone who isn't able to swim at all. A misconception of one's ability and overconfidence in their new found skill can lead to adverse effects. These students may overestimate their capability when they are actually still at "learn to swim" stage.
Thus we always emphasis on, teaching the students to prioritise water safety at this stage of their journey. Here, Chris is being educated on the importance of always looking for a swim aid first if he is in the pool by himself, regardless of the other fun toys in the pool.
Water safety should be educated, not taken for granted!