I believe that means it’s a stereo BLOCK, not stereo effect, necessarily. Meaning that the delay itself isn’t stereo or ‘dual’ but a stereo block will still be able to send a stereo effect THRU the Simple Delay block, which it couldn’t if it was a mono Simple Delay block.
As @xush has stated, it’s more to maintain stereo path when you have one set up. So if you have a stereo modulation first in your signal chain, it’ll still be stereo on the other side of the delay, so you’ll get the L/R panning from the modulation effect baked into the delay sound.
If you want a pingpong delay or something, you’ll have to select an effect that actually does different rates on the L/R channels of the delay.