They say it's different, which I assume means different from any geological formation they have ever seen, including on Earth, but I fail to understand what makes them so mysterious.
Obviously, it wasn't meant for my absolute layman knowledge, but I wish I could have felt a bit of their geological excitement.
The mystery is that on earth these types of structures are the byproduct of a type of bacteria, these are slightly different though the atmosphere of Mars is also not the same as Earth so in that whilst that in some ways point towards a sign of life we still don't know for sure and until we work out with complete confiedience if they were made the same kind of way then we have a wonderful mystery.
This looks like a field of variety sized bubbles in different stages of erosion by sandwind. The large ones across middle path seem to have thinner walls thus faster to grind down than the smaller ones with relatively thicker walls.
http://blog.regehr.org/archives/703
In the top pictures you can see them embedded in the canyon walls. In the pics lower down they've eroded out and are just sitting around.
Correction: moqui marbles are analogous to "blueberries." It doesn't seem clear yet what these new concretions are.