Also, why did it take the missile 25 minutes to cover 40 NM? Was it drawing circles in the air like those bullets and missiles in classic Disney/WB cartoons???
Just because the fishing boat was 40NM away doesn't mean the missile flew 40NM only.
Modern missiles can be programmed with waypoints to fly a circular route in order to attack from an unexpected direction for example.
Also, since the launch was 'accidental', there would not be a real actual target out in the pre-programmed target zone for the missile to hit once it got there (whatever route it took).
It looks on the face of it that the missile then went into some sort of automated search pattern in the target zone until it locked onto something, which happened to have been the unfortunate fishing boat.
What is interesting and worrying is how the missile was allowed to effectively go rouge for 25 minutes.
That would suggest the missile lacks any sort of effective mid-course guidance update ability. If it had such an ability, the ROC military should have been able to effect a self destruct fairly easily and safely by ordering the missile to ditch anywhere in the sea.
The fact that they initially reported the missiles as having caused no casualties would also strongly suggest that they lost track of the missile and didn't know where it had ended up until they heard about the fishing boat.