I don't believe pearled barley is the same type of thing as pearl tapioca.
Pearled barley has been processed an extra step that removes the bran as well as the hull http://www.foodsubs.com/GrainBarley.html, but it still basically looks like a grain of barley.
Tapioca starts out as a big root. The fibrous part is separated from the starchy parts, then the starch is converted into flakes or powder which is then formed into the pearl-sized round balls.