I think it would be difficult for Disney to show that this tweet would be sufficient to bind a user that used the hashtag #Maythe4th. In order to be enforceable, the courts in Meyer v. Uber Technologies, Inc. 868 F.3d 66 (2nd Cir. 2017) gave a two prong test (1) reasonable conspicuous notice and (2) manifestation of assent. These are fact intensive factors. First, Disney would have to show there was reasonable conspicuous notice. The tweet does not have that many interactions (1,057 retweets; 9,678 Quote Tweets; 2,735 likes) so this would like weigh against their argument that a user had notice. Additionally, for specific users, you could look to see if they follow the Disney page.
A manifestation of assent can be difficult to show as well unless the user interacted with the tweet. Just because a user uses the hashtag, doesn’t mean they are assenting to the terms. It could just be because it is a popular saying on May 4th for fans of Star Wars.
Based on this tweet alone, it is unlike you could enforce terms of use and be bound by using #Maythe4th.