One part that is a bit confusing to me is, the original source makes no references whatsoever to any consent form. Usually you can't collect this sort of data without signed consent, and previous reports [0] do mention such a form. I know most people don't read the form, but I'm curious how you can get away with telling someone you're just playing a game and lie so much when the form should clearly state what you're collecting.
Still, there should definitely be better vetting of contractors and stories like this definitely look very bad, even if the intentions were actually to help reduce ML bias.
[0] https://www.engadget.com/2019/07/29/google-paid-for-face-sca...
EDIT: The original article does indeed mention an show a picture of the "agreement".