Seems that after eliminating one of the 3 doors (the goat) and given an opportunity to pick between the two remaining doors presents a new probability as if the game was originally a choice of two... So the "new" probability is 1 in 2 or 50/50...

It doesn't, however change the 33.33% chance that was originally offered...

The wild card here is that the rules change in that, in essence, if the contestant is allowed to make a 2nd choice then the odds of winning the car are 66.66%...

B~