Intel also described the i5-4690k the same way, only up to DDR3-1600. However DDR3-2400 worked just fine.
Same with the i5-6600k. Non overclockable LGA1151 motherboards only support up to DDR4-2133 Mhz. This is not dependent on the processor actually. If you have an overclockable (Z170 officially) motherboard you can OC the RAM up to 3000+ Mhz clock speeds.