The 50/50 probability is just based on historical league wide since the beginning of the 2 pt conversion.(I think the exact number is actually 48%)
I would be interested in seeing the percentage of it if a team solely did 2 point conversions as I do think the numbers a bit screwed since its still considered a special play. And really only done at the end of games with tired defenses
Kind if off topic but college football overtime moves to a 2 pt conversion contest in the 3rd or, so everyone is about to get a lot more info/data on 2 pt trys