Eyewitnesses of the Kabul airport attack claim that many Afghan victims were not killed by the blast but by gunfire from American forces who shot in the crowd.
It would explain why gunfire was reported after the blast. It was only one suicide attacker. So what is the reason to shoot when the only attacker is already dead? Also many victims look like they were shot and trampled to death, not like victims of an explosion
Another point is that most Afghan victims were lying behind the wall and in the sewer, a position that should cover them from just one blast that happened at the gate. Also earlier reports that U.S. forces had a firefight with a second attacker turned out to be not true.