A discharge without a trigger pull would require a malfunction or negligence of almost biblical proportion.

If you drop a weapon, that can lead to an accidental discharge. But there's a difference between a negligent discharge and an accidental discharge.

Now because the weapon was almost certainly a revolver, there is a chance that they were trying to simulate a quick draw with "fanning."

If you remember in those old movies where the cowboy or Sheriff would slap or "fan" the hammer to rapidly cock and fire the weapon, that would be a possibility. It's still intentional. It's the same thing as pulling the trigger.

But having a revolver accidentally go off just from pulling, unless the hammer is already cocked, which it should not be, would be extremely difficult.

Here's a video that explains fanning.

https://www.youtube.com/watch?v=wr0azVhRZUQ