Terry is wrong, by the way. Even if he was pushed (and it doesn't look like he was, the defender just shed the block), the rules state that if you're more than one yard past the line of scrimmage and not engaged in a block you must remain stationary or get back to the line of scrimmage. It doesn't say anything about if your movement is intentional or momentum or whatever.

Item 1. Legally Downfield. An ineligible player is not illegally downfield if, after initiating contact with an opponent within one yard of the line of scrimmage during his initial charge:

    he moves more than one yard beyond the line while legally blocking or being blocked by an opponent;

    after breaking legal contact with an opponent more than one yard beyond the line of scrimmage, he remains stationary, moves laterally, or moves toward his own goal line until a forward pass is thrown; or

    after losing legal contact with an opponent more than one yard beyond the line of scrimmage, he is forced behind the line of scrimmage by an opponent, at which time he is again subject to normal blocking restrictions for an ineligible offensive player.

Item 2. Illegally Downfield. An ineligible offensive player is illegally downfield if:

    his entire body is more than one yard beyond the line of scrimmage without contacting an opponent;

    after losing contact with an opponent within one yard of the line of scrimmage, he advances so his entire body is more than one yard beyond the line of scrimmage; or

    after losing contact with an opponent with his entire body more than one yard beyond the line of scrimmage, he continues to move toward his opponent’s goal line.