What if they are a dummy missile, being used to test anti-missile missiles?
Then they wouldn't have had a terminal-homing guidance system, if it was a target vehicle.
If it was a real system test, it would have been conducted in a different location -- Kennedy Spaceflight Center in Florida, or Vandenburg AFB in California, or out in the Pacific, someplace like that, certainly not in close proximity to one of the most heavily-traveled air and shipping lanes in the world.
And then, if it were a live test of any kind, there would have been NOTAM's issued for aviators and mariners, warning them of the impending activity and giving all parties due advance notice of hardlined exercise areas to avoid.