On Saturday (28 October), Contostavlos criticised Barlow's song choice for Christopher Maloney, before the Take That singer launched a withering put-down by suggesting she had smoker's breath.
The incident caused a stir on the show, and Contostavlos's mentee Jade Ellis - who was ejected from the show on Sunday (October 28) - said she felt the comment was "mean".
Speaking to Heat, former X Factor contestant Amelia Lily said she was surprised by Barlow's comments.
"Gary is normally such a lovely guy so I was shocked. It was a bit out of line. Tulisa's so nice, she's a really cool girl," she said.
Lily added: "The only good thing about that was Louis Walsh's shocked reaction. He's hilarious."
Earlier this week, it was revealed Lily will join Shrek: The Musical as part of BBC's Children In Need.
> Tulisa: 'I'm paranoid about my fag ash breath'
> Jade Ellis leaves 'The X Factor'
> 'X Factor' group single scrapped, winner's single to be for charity?