Thanks for the replies. The release was found in the 'release' position upon inspection post incident. I have checked, with my pistol I am able to turn the lever when the slide is back but the slide wont allow the release of the barrel until it returns to the forward position. I believe that the catch may have been tripped by the shooter. The barrel lock pin has moderate resistance, it does not require overly firm pressure to activate, however it returns to its position positively when released. The lever does require firm pressure to activate, and will not move to the release position unless the barrel lock pin is actuated.
I am considering replacing the barrel lock spring, however I am leaning toward the freak accidental release based on inappropriate grip by the shooter.