This is correct. Retargeting is one of the most valued aspects of adtech.

Manufacturers website contains an iframe to the ad networks website. They signed up for this by placing JS snippet from the ad network on their site that created the iframe. This allows ad network to know that you've visited by placing cookie. Next time you visit site that shows ads from this network they can inspect cookie and show you the retargeted ads.

Could have been FB in this case. Their ad platform definitely allows for retargeting.