I believe you're referring to the pics that were all over the internet and falsely labled as from the December Tsunami; they actually were from a "Tidal Bore" (which is a regular occurance at high tides and the timing is known in advance) going up a river in China; that particular time it was unusually high and people had to flee from their vantage point.
Could be, I wasn't there. I suspect the Japanese learned alot about evacuations during the air raids and really still take things serious. I am serious about that and bet that has a lot to do with it.