It isn't a stupid question at all, it gets confusing because there are dealers selling reflex as a holographic and they certainly appear to be similar, look through both and you can see a difference.
In simplest terms a reflex rifle optic uses an LED projected onto a lens that has been coated to allow only the "red dot" or reticle to reflect back at you as you look through at the target. The quality of the optic is directly related to the quality of the lens/coatings and the LED. Obviously with a lens that is too reflective it is hard to see the target or low relective quality mean poor reticle quality. Shine an LED "laser" pointer at a window and you will see some of the dot reflects back but most passes through; a poor quality reflex will allow the dot to show on the target side also (not good if the target shoots back
A Holographic sight uses a laser to project the reticle patten on the an imagining lens/surface. A real holographic sight is capabale of 3D as well as 2D imagining. This is the technology used for a HUD in aircraft. I believe that EO Tech is the only manufacturer of a true holographic rifle sight (they were the first the technology for rifle sights).