No, in this sense "speed" doesn't mean the speed of light. Instead, it just means that a beam expands quickly--e.g. a short throw in a projector where the image gets big in a shorter distance than in a long throw projector. Nothing to do with the actual speed of light.
If you have a beam of light that expands quickly then each mirror that you bounce it off will have be bigger than the next. What I meant by "slowing" it down was simply change the beam from quickly expanding to not expanding, then stretch the image, then have it expand at the original rate.