MLive.com quoted Peterson, in which he's highly complimentary of Stafford and what Peterson calls his "baseball throwing."
By that, Peterson means that Stafford has many different ways to deliver the football. He says that Stafford has different throwing motions to get the ball out of his hands, which can be beneficial for a quarterback who is trying to keep the defense on its toes.
It's hard to key in on when the ball will release and where it's going if the quarterback is using a throwing motion different than the one you're used to. In film study, players look very closely at all of that stuff, and it's clear Peterson has been doing his homework.
More than that, Peterson is complimentary of Stafford in general, calling him "one of the better quarterbacks in this league." He'll get a chance to play against Stafford on Sunday when the Cardinals host the Lions.