Either him or they're trying to create hype because they know people would automatically think of him by saying everyone would be "shocked"
Has it been confirmed that the person is a guy? If not Chris then I would say Beyoncé. Everyone swears they hate each other so it would be kind of shocking to see them collaborate, especially on a song like that.
She said on twitter that she was looking for a male to be featured on the song.
If the confirmed artist is a male then it has to be Chris. No other male rapper/singer would be a "shock" to anyone unless they're just trying to **** with people and create more hype.