Title is definitely malformed on this one, a quarter of US adults have a Twitter account of which the top 25% most active US adults produce 97% of the tweets.
A quarter of (US adults on Twitter) account for 97% of tweets
That seems to be based on this result from the article:
An analysis of tweets by this representative sample of U.S. adult Twitter users from June 12 to Sept. 12, 2021, finds that the most active 25% of U.S. adults on Twitter by tweet volume produced 97% of all tweets from these users.