GR translation: a phantasmagoria, a real one

[Mike Jing]

V12.32-38, P13.7-13   Accompanying will be a phantasmagoria, a real one,
rushing toward the screen, in over the heads of the audiences, on little
tracks of an elegant Victorian cross section resembling the profile of a
chess knight conceived fancifully but not vulgarly so—then rushing back out
again, in and out, the images often changing scale so quickly, so
unpredictably that you’re apt now and then to get a bit of lime-green in
with your rose, as they say.

Here we are talking about the projector (magic lantern) moving rapidly back
and forth on little tracks, is that correct?

I'm asking because the published translation offers a completely different
interpretation.

Also, why the emphasis on "a real one"? As opposed to what?