the devs created some "easter eggs" in the game for fun so at times you would come accross them and be surprised
most were removed by the big mods because they were non realistic so things like the smiley faced radar contacts were taken out.
the flying dutchman seamed to be a favorite by most so if any easter egg was left in the game i think it might be this one.
its often moving at a good 15-20 kts so you cant keep up with it and it has no damage model so you cant hit it with anything, all you can do is look at it as eye candy