They are broadcasting a mix of high-definition channels, including four channels in 4K, two in 1080p, and eight in 720p, all on a single RF channel. Viewers can experience some of the benefits of ATSC 3.0, like higher resolutions, without needing a new ATSC 3.0 compatible TV or tuner.
If you click through to the full interview, the owner of the station (who bought the station for a place to test his ideas) says there are even some fringe benefits, like increased effective range.