Well yes there is reflection, but also transparency, otherwise how is this a glass shader?
The point is the density that masks this transparency is top down, not coming from 360 degrees of the objects surfaces.
In the example image we have a luminous floor with lines, so we can distinguish actual features. I'm not sure a solid luminous floor would allow that.
You can plainly see the lines following Z go through the object perfectly aligning to the lines behind the object (as they're the same lines). If they were a reflection, they would lean the opposite way and not aligning with the lines behind the object (wouldn't they? These surfaces aren't straight), as they would be mirrored reflections. No, we're seeing the line through the object, because the density is only from the top of the object down to the bottom, and the glass is producing glass transparency.
In a side note, it's very concerning that a "shadow" can dampen a "luminous" shader (the spotlight is still on from above)....... o.O