I have a feeling that that is because refined sugar is absorbed in a different manner than the sugar in juice. Just speculation though.
A raw orange is 31-40.
Orange juice is 46-54.
Coca-cola is 63.
I think juice may be a _LITTLE_ better than soda. I still choose to drink neither, and think I am better off for it.
You're making a very good choice. I would encourage you and others to consider the raw oranges 31-40 GI as, itself, very high and akin to something like dessert or a special treat.
Or, to expand on what a child of your post expressed:
soda < juice < fruit < ... < ... < vegetables/nuts