They shoehorned McSweeney into opening as they did with Aaron Finch six years ago. Although Finch was an opener in the white ball formats, he was a middle-order bat in First Class Cricket (Sheffield Shield, County, etc.) like Sweeney.
I'd like to think Sweeney could still have been slotted into #6, especially as they're getting virtually nothing out of Mitch Marsh with either bat or ball. (Even though anyone at #6 is only really a placeholder till Cam Green regains full fitness.)