I just watched cake boss, and after he had assembled his fondant cake, he was steaming it - why? Is that what makes fondant shiny?

yes...I always steam...

Yep it makes it shiney...I have never done it!

Oh!! I thought he was doing it to get the fondant swags to stick.

if you look at a close up of the bed in my aurora cake, I steamed that so the bed is shiny...also the black and white cake...

I've steamed gum paste flowers but not fondant...

Yes, steaming makes it shiney for sure. I haven't steamed a cake though.. I have steamed my gumpaste flowers to fasten the powder coloring/ dust colors to the petals.

Steaming makes the fondant shiny but it also makes it a bit sticky while still damp so that you can add decorations.

I always steam my fondant cakes with a hand held clothes steamer and while it does make it shiny that shine does tend to lessen when it dries. It also seals luster dusts and shimmers and makes everything look satiny and finished.