Understanding jit.histogram values

I've looked at the jit.histogram help file, and I understand that each cell index in a 1D jit.histogram matrix is equivalent to each possible R, G, or B value—a value in the 3rd cell (index of 2) of a jit.histogram matrix plane indicates that pixels in that plane are set to 2. Can someone explain what that value actually means though? I would've expected that it referred to the number of pixels in the incoming matrix that are set to that value but after messing around with the help file, that doesn't seem to be the case (unless I'm missing something).

Thanks!