That is the colloquial definition of a double tap.

That is not automatically the case whenever two missiles strike a target.

The "follow up" hit requires a delay. The delay is not accidental - you want to give time for a crowd to gather.

All targets in the area received >= 1 missile, and all somewhat close together, from the NYT analysis.

Well that's exactly what happened. US hit the building and many died. All the surviving students and teachers rushed to a prayer hall for protection but almost exactly 40 minutes later US airplanes (not surface missiles) hit the building again.

All of these facts are outlined in US' own internal investigation and in the UN's fact-finding mission.