that's sort of true and sort of false. here the origin is plotted in the upper-left-hand corner, and in the 2d fft images you're used to looking at, it's plotted in the center instead. but you can plot the dct that way too, so it's sort of false

it's sort of true in that if you plot the standard 2d fft in this coordinate system, the data will be concentrated not in one corner of the image but in all four of them. the dct really is unusual in putting all the low-frequency stuff at positive frequencies instead of equally at positive and negative frequencies