Kelvin was a dude, but now his name is a unit of temperature.  1 degree Kelvin is equal to 1 degree Celsius.  The use of Kelvin temperature units to measure light color comes from the change in color of an object (old fashion tungsten filament) as it gets hotter.  As a tungsten filament starts getting hot, it first glows red.  Hotter still (about 3000 degrees Kelvin) it looks warm white.  Hotter still it would look blue - but tungsten melts before that.  LED color is not determined by temperature as the mechanism of creating light is different.  Nevertheless, manufacturers continue to use the old standards applicable to tungsten filaments.  LED's can have a wide range of color temperatures not achievable with bare tungsten source.