A US Central Command investigation found that an aid worker and nine members of his family, including seven children, died in the 29 August strike.
The youngest child, Sumaya, was just two years old.
The investigation found the man’s car had been seen at a compound associated with IS-K, and its movements aligned with other intelligence about the terror group’s plans for an attack on Kabul airport.
At one point, a surveillance drone saw men loading what appeared to be explosives into the boot of the car, but it turned out to be containers of water.
Gen McKenzie described the strike as a “tragic mistake”, and added that the Taliban had not been involved in the intelligence that led to the strike.
The strike happened as the aid worker – named as Zamairi Akmadhi – pulled into the driveway of his home, 3km (1.8 miles) from the airport.
The explosion set off a secondary blast, which US officials initially said was proof that the car was indeed carrying explosives. However the investigation has found it was most likely caused by a propane tank in the driveway.
Relatives of the victims told the BBC the day after the strike that they had applied to be evacuated to the US, and had been waiting for a phone call telling them to go to the airport.
But more than that, this catastrophe exposed the dreadful human cost of a war that had been fought largely from the air for years.
That it should take place just as the Americans ended their 20-year occupation will cast an even darker stain on the chaotic US exit.
But for some in the region, it is a particularly stark example of the ongoing dangers of drone warfare.
It sparked a mass evacuation effort from the US and its allies, as thousands of people tried to flee. Many were foreign nationals or Afghans who had worked for foreign governments.
The security situation was further heightened after a suicide bomber killed up to 170 civilians and 13 US troops outside the airport on 26 August. IS-K said it had carried out the attack.
Many of those killed had been hoping to board one of the evacuation flights leaving the city.
More than 124,000 foreigners and Afghans were flown out of the country before the deadline. But some people were unable to get out in time, and evacuation efforts are ongoing.