Fumed silica and silica fumed are two different terms for two substance. They are both silica dioxide. On some occasions people confused with them. They have different derivations, technical characteristics, and applications, then the price is different.
Fumed silica
Fumed silica, also known as pyrogenic silica because it is produced in a flame, consists of microscopic droplets of amorphous silica fused into branched, chainlike, three-dimensional secondary particles which then agglomerate into tertiary particles. The resulting powder has an extremely low bulk density and high surface area. Its three-dimensional structure results in viscosity-increasing, thixotropic behavior when used as a thickener or reinforcing filler. -Via wikipedia