The oarfish, the article explains, is just one of many folk tales involving mythical animals as harbingers of (and sometimes as the cause of) natural disasters—particularly earthquakes and tsunami. A Japan Times article explains a possible (though not proven) causal link as:
I wrote a piece earlier (here) about the predictive nature of folklore and how those that went before us have tried to help warn us of potential danger. It’s easy to dismiss these tales as the simplistic ways our predecessors have tried to explain the natural world around them. And I’m not suggesting the downright panic the oarfish sightings have generated in some is justified. But, as I pointed out in the earlier piece, it’s worth letting even something as odd as a strange fish appearing in a fisherman’s net be the impetus to encourage better planning and preparation for a disaster we know is inevitable in the region at some point in the future.