Is it true the sign language interpreter at Mandela's funeral was a total fraud?

I just heard that there was someone signing at the funeral and he was just waving his hands around in made up motions. How the heck did they let that happen? If it is true the entire recording of people eulogizing Mandela has someone standing next to them who is not who he said he was, and who made his way into this very important ceremony with heads of state from everywhere.

Did you hear about it? Do you have any details? What do you think about it?