A Syndicate court grants Carl the honorary title of Earth's de-facto native leader, empowering him to sign interstellar agreements.
Rishi reveals that Syndicate law dictates that when a planetary body has no working government, a native leader is chosen by multiple factors. Though other military groups on Earth's surface would seem better suited, and other in-dungeon entities could plausibly claim the title, Carl's status as a Warlord and the number one crawler on the Leaderboard makes his claim legitimate. No formal leadership claim had yet been filed, so the naga petitioned on Carl's behalf while drafting their treaty, and the court granted the petition.
The position is described as mostly honorary, but it makes Carl a signatory on Earth's behalf — enough to make the Naga Treaty Offer legally binding if he signs it. Carl's reaction is disbelief and derision ('Leader of Earth? Are you smoking crack?'), and Rishi suggests a Crawler Attorney could explain the particulars. Carl never signs.
The legal fiction that lets Rishi treat Carl as a head of state.