It was true that they were different, but now isn't.
Up until about 6-8 months ago, there were a few differences between the two. The Bambinos had a front elastic waistband, while the X-Plus did not, the obvious difference in prints, and the Bambinos had a marginally higher cellulose content (making them ever so slightly thicker).
Today, they are the exact same diaper. The X-Plus now include the front waistband just like Bambinos, and there is absolutely no difference in construction aside for the difference in prints on the tape landing area, and the lack of a wetness indicator on the Bambinos.
I have both in my possession currently... They are identical.