When Rojan reduces Shea and Thompson, the camera work deliberately shifts position of the cubes so we don't necessarily remember which was which. Shea is restored but Thompson isn't.
Both were equally nonessential to Rojan so both were picked. After seeing this episode umpteen times I just asked myself yesterday: did Rojan deliberately select her? Or, being both nonessential, did he simply randomly act without remembering which was which? I'd steer towards random unknowing on his part. What say you?