The Boston Whalers are not radar equipped, and had to be vectored to the US boats. It is very likely they were tracked down and confronted with overwhelming firepower from one of these fast Iranian patrol boats:
And the BWs were used for stopping and boarding the US boats.
But that still suggests that the US failed to provide air cover, or really try to stop the seizure. Had an F/A-18 arrived on scene, the patrol boat would have been on the losing side of the overwhelming firepower equation, and they would have known it. The chance of a ship evading a modern laser guided bomb is nearly zero. Nobody on that patrol boat would want to bet on being able to control the damage caused by a Hellfire missile hit followed by a couple of direct hits by 500 lb bombs, or even a few good 20mm cannon runs.
Also, it is almost unimaginable that the carrier group, or the 5th Fleet Command isn't tracking the location of the patrol boats. I can imagine a couple of Boston Whalers sneaking up on a US boat, but those larger combat ships should be under continuous tracking. The whole area is quite small, the boats were only about 120 miles from 5th Fleet Headquarters, and there are land based aircraft about 25 miles further away.
I doubt we'll know what really happened for a long, long time.