They are extracting silica from rice hulls. They can say it's a rice product because the silica is from the hull.
Here's some info from
wiki:
"Rice hulls are the coating for the seeds, or grains, of the rice plant. To protect the seed during the growing season, the hull is made of hard materials, including opaline silica and lignin. The hull is mostly indigestible to humans. During the milling process, the hulls are removed from the grain to create brown rice, the brown rice is then milled further to remove the bran layer to become white rice. The very high content in amorphous silica of the hulls confer to them and to their ash (SiO2 ~ 20 wt.%) after combustion very valuable properties."
Yes it is natural but I am looking at other options. This is nothing new! Silica and silicon dioxide have been used for years. It works so you should have no problem with this product. I don't really like it in rubs so I'm looking at other options that are actual food products.