Based on Marshawn's track record, I doubt this story is fabricated at all. This is the same guy who allegedly brought his own booze into bars ... I mean, who even does that?
He is a punk, and he is at best a marginal NFL back. We can get anyone to back Freddie up that will do an as good or better job (what was his YPC?) Ask yourself, if he got every carry Freddie had this year, would he have topped 1,000 yards?
I'd chalk him up for 600 yards max.