Are you familiar with
Diatomaceous Earth?
You might notice on bags of food/garden grade DE, the ingredients label says something like "85% Silicone Dioxide".
Similar thing with the Fulvex, I would say. It contains 1% Mg derived from Magnesium sulfate, but the product itself is more than that. Fertilizer labels are governed by law and they can be strange. AFAIK they aren't actually allowed to put "fulvic acid" as in Ingredient on the label, as it isn't considered a plant nutrient or whatever the case may be.