It was designed to be “cocked and locked”
There is no safety that blocks the hammer from the firing pin with one in the pipe and the hammer down.
The grip safety disables the trigger mechanism
Its apparent the gun wasn’t dropped on the hammer, because the bullet ended up in the floor.
Since the gun was purchased at a surplus sale, they may have wrongly ASSumed that someone checked to see that it was unloaded before putting it up for sale?