I wish articles like this would be more technically vigorous.

What actually happened here? Was the Facebook app uploading every photo on your phone in order to run a bit of ML to help recommend images that might be a good fit for specific posts? Were they doing ML stuff on the device directly? Were they doing anything else with the photos aside from powering this "suggested image" feature?

I get that Rapporteur.com might not be the best venue to answer these questions, but I'd be shocked if any coverage of this story got into the details of how this stuff actually worked.