The Girls Aloud star, who is co-managed by will.i.am, performed her new solo single 'Call My Name' on last weekend's semi-final show.
Cole reportedly pledged to sing live on the programme and her representatives later confirmed that she "sang live with a backing track".
"I was there. She wasn't miming," the Black Eyed Peas star and The Voice coach told Metro.
He added of Cole's performance: "I didn't know she was jumping on stage until she did. I thought it was dope."
Of her chances of breaking America, will.i.am said: "America's a weird place right now, in terms of breaking.
"I don't know who is breaking America right now. We never broke America till after.
"You gotta break around the world. As an American act, why am I doing a show in the UK if I care about breaking America?"
The Voice UK semi-final results show - photo gallery:
Copyright: BBC Wall To Wall