This answer is correct because these are the two factors that affect the heat island reduction potential of the materials. The SRI is a measure of how well a material reflects solar radiation and stays cool in the sun. The higher the SRI, the lower the surface temperature and the less heat absorbed by the material. The unbound percentage of the open-grid pavement system is the ratio of the area that is not covered by the paving material to the total area of the system. The higher the unbound percentage, the more permeable the system and the more water infiltration and evaporation, which also reduce the surface temperature. The vegetated roof system does not need to have a specific SRI value, as long as it uses native or adapted plant species that provide shade and evapotranspiration. The open-grid pavement system does not need to have a specific SRI value, as long as it has at least 50% unbound area.
References: =LEED v4.1 OPERATIONS AND MAINTENANCE - WAP Sustainability Consulting, page
26;SpecTopics: Heat Island Reduction Credit and LEED V4/V4.1 - Carlisle SynTec;LEED AP O+M - Heat Island Reduction - GBES