The jet was pointed at the F-117s across the field but the missile hit the ground a little way in front of the jet because the rails slope down when it's on the ground.
It happened during an "alert turn" when they were swapping out the alert jets. They warm up the incoming set, pull the pins and set it up for the five minute alert. Most of the armament safety pins are removed during this warm up so if there's an actual alert launch they don't have to stop at the arm area on their way to the runway, they just go.
Anyway, while the jet was running, the weapons guy pulled the Sidewinder's pin and it immediately launched. The guy (minus eyebrows but otherwise unhurt) said he thought the whole jet blew up.
It was caused by a faulty power supply in the missile rail. They found a number of them with the same issue in the supply chain during the investigation.