Ok, so I only have watched 1 episode and this situation really bugged me.  I think the way I see it,  both the pills are poison, the game is getting the people to take a pill.  Obviously even with the gun turning out to be fake the Cabby still manipulated Holmes to going that far with the pill.. His previous statements all still line up with the real game being getting the people to take the pill. "He knows how everyone thinks"  There was no "Gun or Pill" win either in this scenario as the gun is only a prop to get them to chose a pill.  The real way to win was to not even pick. The Cabby wanted control and he wanted to intrigue Holmes enough to make sure he "won".  The only real way to break people like that is to not allow them to manipulate you. Think trolls here as well, they love it when they can a reaction but have more issues when you just straight up wont take their crap and call them out.  ( at least in my experience this has been the case) 



Also to note: The Cabby was no threat to murder someone in cold blood.  His whole emphasis and thrill was that he only "talked" to people and they committed suicide. If he kills outside of that context it hurts his ego and it ruins his "high" or "thrill" he gets from it.