The wave was caused by a meteor impact
It was an ocean strike, miles away.
- Pretty much Jossed; it was an earthquake (i.e. subsea displacement) that generated the rogue wave. The ship was close to the fault line (and in relatively shallow water) when it went. Poseidon had almost no time to react, and the wave was still very, very high when it hit the ship, rather then the barely noticeable, extremely fast form tsunamis typically take in the open ocean.