This is one of test for red cross lifeguard training. However in real life it is much better to spot drowning victims than video.
Yeah having a perspective that is so different from the lifeguard does make it really hard.
This is likely perspective you have while also browsing HN on your phone. That's the whole point - it's really hard to spot one unless you are looking for him, have training and are positioned properly.
Being distracted by your phone and not seeing a drowning child is different from paying close attention to a low-res 2D image and not seeing a drowning child. You can't fully train for one by practising the other.