I think he's trying to cement Harris, Hoilett and Manga into the team (Manga was impressive) and wanted to avoid a tonking (like we had this time last year under Slade) by putting Halford in front of the back four as a shield (as when Rotherham did a job on Wednesday last season).
I agree it was a conservative and safe selection - but I think there were good reasons.
What I can't understand is why he didn't start with Fred! You remember Fred? Our 'No 9'.