There have been several studies that have found evidence of foot problems creating low back pain. They call this issue "Serial Distortion" meaning in simplistic terms, the foot bone is connected to the leg bone, the leg bone is connected to the hip bone, et cetera.
All silliness aside, any joint in the lower extremity that isn't doing what it is designed to do will affect the performance of the joints above and below it. The lower extremity is called a closed kinetic chain as the earth is on one end and gravity on the other, this is why it is important for every joint in the lower extremity to do what it is supposed to do.
A proper pair of functional orthotics can assist with the mechanical function of the entire lower extremity hence its ability to affect low back pain.