It uploads them in whatever order they are given to CB Gallery by the field input. For example I've the below files.
photo_1.jpg
photo_2.jpg
photo_3.jpg
If I just do a select all it'll upload 1, 2, and then 3. If I manually select 3, 1, and then 2 then it will upload in that order. They are then displayed based off their datetime upload timestamp so usually reversed of whatever you selected.
In short the upload order has nothing to do with CB Gallery; either your filenames are not in the order you want them to be when selecting all or when you're manually selecting them you're doing so out of order.