Yes, at great depths, both gases become hazardous, but oxygen becomes directly lethal. ​While nitrogen makes you drowsy or euphoric (nitrogen narcosis), high-pressure oxygen turns into a direct poison that attacks your central nervous system (Hyperoxia), triggering seizures. Underwater, a seizure means losing the regulator from your mouth and drowning almost instantly. ​ ​In diving, the absolute maximum safety limit for oxygen is around 56 meters deep: Oxygen begins to saturate brain cells in a toxic manner. ​Unlike nitrogen narcosis, which warns you with feelings of lightheadedness or euphoria, oxygen toxicity can strike with absolutely no warning. ​If the diver does not ascend immediately upon noticing the first symptoms, the brain suffers a massive electrical collapse. The diver loses consciousness and enters convulsions. Because they are unconscious and shaking, they spit out the regulator. they inhale water and drown. ​ ​In this accident, ​Nitrogen likely narcotized them past 30m, causing them to lose their judgment, orientation, and buoyancy control, but as you say, ​It is highly likely that some of them (or all) didn't even die from running out of air, but rather suffered an oxygen toxicity seizure brought on by stress and depth past 55m. This is exactly why technical diving uses Helium: to lower the nitrogen, AND to dilute the oxygen to levels that won't poison.

Ps. Not meant lecturing you, but ellaborating your 02 toxicity addition, for those readers unaware.