So what? A registered agent is literally the agent registered to accept process service. The registered agent is clearly not the corporate headquarters, a branch office, or anything other than a business whose purpose is to accept lawsuits, subpoenas, and other legal and official notices.
Well, that's the same thing the NPR article is reporting on, which is the equivalent legal concept in Panamanian law.
Polymarket's actual offices are remote-first, but they have a small space set up in New York City which is the closest thing they have to an HQ. It's basically set up like a coworking / hotel sort of space.