I don't think that's true in the sense meant. Sure, to reproduce a near replica of a specific brick from first principles. But not to produce something broadly functionally equivalent. You can (rather inefficiently) manufacture approximately equivalent bricks in your backyard on your own, possibly even from locally harvested material depending on where you live.
Well. Sure. If we move the goal post to “something passable and good enough” you only need a small number of people. In that sense, we are lucky that “black smithing” (as a proper trade) only ended in the last hundred years and many people continue it as a hobby. In that case, “small team of hobbyists” can likely reproduce a few bricks. But bootstrapping mass production of bricks? Unlikely.
