Even if the wave isn't very tall, if it is fast-moving it can knock you off balance. Once you're down, wave doesn't have to be very tall to drown you. There's a

Even if the wave isn't very tall, if it is fast-moving it can knock you off balance. Once you're down, wave doesn't have to be very tall to drown you. There's also the fact that rip currents are commonplace phenomena on beaches all over the world, so you combine that with a single unexpectedly fast wave and it's easy to believe a few people would die.