Unless there is video of the shooting, we are unlikely to know whether the rumors are true.
1) The victim cannot testify. Even if he could, human nature is likely to mean he would blame the gun rather than his own actions for the ND.
2) The fact it was pointed at his chest suggests overall poor training.
3) If there are any eyewitnesses, all eyewitnesses knowingly or unknowingly make false statements. People do not take in information like video cameras. We take in part of the information available and gap fill in missing information.
The Air Force has the actual gun and holster available for testing. What if they cannot replicate the "it just went off" in the holster scenario?