The League's letter to Rice giving him official word about his suspension says that that the additional sanction was because the video showed a substantially different version of events than had been portrayed in the meeting with Goodell, League officials and the team.
Which, going back to our six stages of hypocrisy list, means that League officials who viewed the video at the casino (and received and watched their own copy of the video) managed not to convey the actual events very accurately to their superiors, if at all. If that was true, you might think someone would face sanctions themselves for failing at their job. We'll probably have to wait until a Friday news dump in April to get word from Mueller's investigation on that.