From a quick internet research - They got stem cells from some other part of somebody's body and somehow "reprogrammed" them into pluripotent (iPSC) stem cells

From a quick internet research - They got stem cells from some other part of somebody's body and somehow "reprogrammed" them into pluripotent (iPSC) stem cells which can then make other cell types. They made brain cells with them. Also, the organoids are 0.5 mm diameter balls.