If you look carefully at the photograph of the under-belly of the aircraft you see that three gears are extended normally but the right hand wing gear is blocked in the wheel well by what appears to be a substantial white sheet of material that has jammed between the open wing gear door and the truck asssembly.
Some video that has been released shows a shower of sparks from the underbelly area of the aircraft on touchdown. This would have been the bottom edge of the wing gear doors contacting the runway during the flare? Once the nose was lowered the contact stopped.