Carrying without a holster can be done safely. My grandfather used to carry a single-action revolver in his pocket. Perfectly safe because it was a single-action and the hammer was down. You can carry the S&W M&P involved in this incident in condition 3 with no holster and it will be every bit as safe (and probably a bit safer from a drop safe perspective).
What you can't do without creating a much higher risk of negilgent discharge is carry a safe-action pistol in Condition 1 with the trigger exposed.