Disco dust is probably what they used. It's available on the internet at cake supply vendors.
To clarify the person who said that's not OK to eat. Disco dust is plastic. I agree with Leah , you can find very pretty sparkling sugar colors and use a lot of it. I do not put disco dust on anything that someone will consume. Just because Elmers glue is non toxic does not mean I'll use it on a cake;)
It's disco dust. You can just tell. In the parts of the picture that aren't blindingly reflective,you can you still see light bouncing off of...plastic.
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