United Healthcare did not respond to multiple requests for comment, and TeePublic also did not respond to a request for comment. It is theoretically possible that another entity impersonated United Healthcare to request the removal
In the absence of a claim to the contrary, given they've had more than enough opportunity to deny it, I can only assume that United Healthcare is in fact making these illegal and fraudulent takedown requests.
If you draw a picture of him and then someone else posts it without your permission, then yes you'd be able to claim your copyright was violated. Copyright is something that automatically applies to any creative thing someone produces. You can't use someone's name/likeness to sell a product unless they've given you permission, but that's not a copyright claim.
These claims sound like abuse of the DMCA takedown system.
From my non-lawyer understanding, copyrights on a photo reside with the creator of the photo, however, the person who is in the photo would have some ownership of their likeness kind of like a trademark where you would have to argue for rights to the use of it.
So basically the only people who could really claim anything would be the owners of the security cam for that pic that everyone has latched onto.