Watch the clip you imbedded. Hitchens did not push his shoulder. His hand might have been contacting Pettigrew’s shoulder (still not absolute in that clip), but there was no material impact of that preventing Pettigrew from catching the ball. The vast majority of fans, particularly Lions fans, cry PI because Hitchens doesn’t play the ball. But face-guarding is not illegal and hasn’t been for probably 2 decades. Face-guarding will be called PI if the defender is bumping, running into or making material impact with the receiver. Hitchens wasn’t; he’s not against Pettigrew’s body. In a way, Pettigrew helped Hitchens’ separation by extending his arm on the face-mask.
By the way, that’s the difference between that play and Brown’s against LV on Thanksgiving. Brown got called because he was into the receiver’s body.