You're right, but the tsunami released a lot of debris to the sea near Japan, and the sea creatures where slowly transported for thousands of miles, on that debris:

"Between June 2012 and February this year 289 Japanese species attached to 600 pieces of debris washed up on beaches in the states of Washington, Oregon, California, Alaska and Hawaii, as well as in the Canadian province of British Columbia, according to the study."

It's not the waves that move matter, it's the ocean currents and winds (for objects buoyant enough to act like sails).