I think he means if he squeezes the trigger slowly, a small amount of pressure allows the hammer to fall, but the movement isn't enough to clear the hammer block (transfer bar) so the hammer strikes it rather than the primer and the gun doesn't fire. If you jerk the trigger, or use double action, the bar clears so the hammer strikes the primer and the gun fires.
I'm assuming this revolver has the relatively modern hammer block that keeps the hammer from striking the primer unless the trigger is pulled sufficiently.
I would guess that through wear, or more likely, a bad trigger job that gave it the hair trigger, it just needs to be returned to stock. Adjusting the bar so it disengages with a very light trigger pull may make the gun unsafe.