My prayers still are focused on the young man and his family.
My son, several years ago was a CP, a lifeguard. They use the training system Ellis. Ellis uses a constant scanning routine system. If you stop and watch those lifeguards, follow the patterns their heads take as they watch the water. Disney's lifeguards are all retrained when hired, my son did a solid week at Mickey's Retreat of 8 hours a day just to retrain to Disney's Ellis program. Beyond the pool training they are certified in extensive emergency training, from choking, first response to heart attack, seizures, spinals until EMTs arrive. Ellis requires 4 hours of back up training per month from certified Ellis trainers to keep their skills sharp.
It tends to make me lean towards there wasn't lifeguards at the pool at that time, because even if the lifeguard missed the child go under the lifeguards would have been likely the ones that would be performing the CPR until the EMTs arrived. My DD is an Ellis Trainer, she trains and certifies lifeguards, she stated that it is protocol for lifeguards to take over rescues until EMTs arrive.
Rule of thumb, never swim alone, no matter what the age is.