Sounds like it could be an airport-run thing where they just open it up to all elites.

MSP has a similar line - there's the Delta-controlled elite security line (which is only Gold and up), but there's another checkpoint 150 feet down at the United counter that is open to any elite of any airline (including Delta Silvers) - this line is often faster during peak hours since there are so many Sky Priority customers, while not a ton of elites on other airlines.