In the space of 24 hours this week, the U.S. military went from planning for a possible mass evacuation of Iraqi refugees to declaring that there was, in fact, no imminent crisis. What happened? Did the Pentagon misjudge the situation on Mount Sinjar, which only days ago was being reported as a site of a potential genocide?

Navy Rear Adm. John Kirby, the Pentagon press secretary, said Thursday that conditions on the mountain range became clear only after a team of about 20 U.S. Special Forces landed there early Wednesday and were able to observe the situation firsthand. After spending the day on site, the mission team estimated that there were between 4,000 and 5,000 members of the Yazidi sect in the area – and that about half of those were actually refugees, Kirby told reporters.

Contrary to fears that tens of thousands of refugees were without food or water, the Special Forces also concluded that the Yazidis were no longer at imminent risk of hunger or dehydration, thanks to a weeklong U.S. campaign to drop relief supplies by air. As a result, the Special Forces re-boarded their aircraft, flew back to their base in the northern city of Irbil, and reported to their superiors that there was no need to organize an evacuation.

So did the Pentagon misjudge the situation? Kirby said no, that there was no doubt that tens of thousands of Yazidis had already left the mountain range on their own, or with the help of Kurdish “pesh merga” militia forces. He also said that about a dozen U.S. airstrikes against Islamic State fighters – who had been threatening to massacre the Yazidis – had helped to stem the crisis.

“We believe that the threat of mass violence on Mount Sinjar has passed,” he told reporters Thursday afternoon at the Pentagon. “We believe that the risk of genocide was real. I mean, we were at the outset talking tens of thousands of these refugees who were being chased and slaughtered and fired upon.”

The Pentagon has said it has been conducting between 50 and 60 reconnaissance flights a day over Iraq, many of them by surveillance drones. So why couldn’t the drones – which are equipped with powerful cameras — tell that there were no longer huge masses of refugees on Sinjar?

Kirby suggested that is because drones aren’t as omnipresent or omniscient as some people might think. “We made the best estimates we could based on the limited picture we had from the air,” he said. “It’s very difficult to do nose counts from the air…I mean, it’s just an imperfect science.”

Although the danger level on Mount Sinjar has ebbed, Kirby noted that numerous other refugees have fled Islamic State as its fighters have swept across Iraq and warned that there was still a strong risk that other humanitarian disasters might erupt. He said the Pentagon would withdraw some troops from a 130-member team that had arrived in Iraq on Tuesday to assess the refugee crisis, but said an unspecified number would remain in case trouble crops up elsewhere.