I do not think it was interference. Butler was making a play on the ball and he didn't go "through" Lockette's back. Here is the NFL rule:
Actions that constitute defensive pass interference include but are not limited to:
(a) Contact by a defender who is not playing the ball and such contact restricts the receiver’s opportunity to make the catch.
(b) Playing through the back of a receiver in an attempt to make a play on the ball.
(c) Grabbing a receiver’s arm(s) in such a manner that restricts his opportunity to catch a pass.
(d) Extending an arm across the body of a receiver thus restricting his ability to catch a pass, regardless of whether the defender is playing the ball.
(e) Cutting off the path of a receiver by making contact with him without playing the ball.
(f) Hooking a receiver in an attempt to get to the ball in such a manner that it causes the receiver’s body to turn prior to the ball arriving.
Actions that do not constitute pass interference include but are not limited to:
(a) Incidental contact by a defender’s hands, arms, or body when both players are competing for the ball, or neither player is looking for the ball. If there is any question whether contact is incidental, the ruling shall be no interference.
(b) Inadvertent tangling of feet when both players are playing the ball or neither player is playing the ball.
(c) Contact that would normally be considered pass interference, but the pass is clearly uncatchable by the involved players.
(d) Laying a hand on a receiver that does not restrict the receiver in an attempt to make a play on the ball.
(e) Contact by a defender who has gained position on a receiver in an attempt to catch the ball.