The green box around his face in the image is evidence that it detected a face, but not that it had collected or stored identifying biometrics. It would be legal for a POS device to detect any face, e.g. to help decide when to reset for the next customer. But as I understand it, this would usually be enough to trigger discovery, where he could learn the necessary technical details. Even if this suit fails, the store…
Answer: File a lawsuit and use discovery to find out.