It's definitely the city-brake system (in Honda-speak, it's called CTBA). In the online manual, p.108 shows the indication, pp 450-454 explain the system in more detail.
NB those page numbers are for the online manual, they may be slightly different in any version you're looking at.
Basically, it's a low-speed system that detects an obstruction ahead of you (not behind) and first warns you, and if the hazard persists and you don't take avoiding action, it'll apply the brakes.