The Niro earned this score by getting a "Good" rating, the highest IIHS bestows, in every single crash test, including the difficult small overlap test for both passenger and driver. It also received a "Good" rating for its optional HID headlights, and the optional forward collision prevention system managed to prevent a collision at speeds up to 25 mph.
This brings us to a caveat to the Niro's scores, though. The highly rated headlights and forward collision prevention system are options that don't come standard on base models of the Niro. The headlights only become available on the second-highest EX trim, and are standard on the top Touring trim. The forward collision prevention system is not available on the base FE trim, but it is an option starting with the second-lowest LX trim, and is standard on Touring.