Many cosmetically coated pharmaceuticals also use TiO2 in the coating formulation, to make the coating nice and shiny white. Iron Oxide is another common pigment used for coating tablets and pellets.
If they wanted sediment, it would be cheaper to just add some of the actual fruit sediment they already have from earlier in the juicing process, rather than purchasing another ingredient.
Are you sure it isn't used for the opposite reason? Silicon Dioxide (silica) can be used as a suspending agent, so seems like it may have been added to prevent the natural sediment from collecting at the bottom.