The N-Dubz star claimed that the four-piece - comprised of Jesy Nelson, Perrie Edwards, Leigh-Anne Pinnock and Jade Thirlwall - had managed to break the "girl band curse" on the show because they had a genuine friendship.
"With these girls, there was always something different about them. You could see how genuine they were from the start and it didn't feel like a group of girls just put together," Contostavlos said on The Xtra Factor.
"They were friends. It's everything from the talent, to the friendship, it's real and it's something that's been missing."
She continued: "I think there has been problems in the past with girl bands being misunderstood and people not really getting to know them."
Little Mix will be in next week's semi-final alongside Marcus Collins, Misha B and Amelia Lily.
> Janet Devlin voted out of The X Factor
> Little Mix top Digital Spy poll
> X Factor Little Mix: 'We want to be a modern Spice Girls'