Employees at Twitter would go to jail if they used Twitters information to trade. Journalists have gone to jail for sharing information about stories they are writing to third parties.

But it is possibly legal for Twitter the organisation to do that or sell tweet "firehoses" to third parties.

I would not be surprised if they had deal with with traders that gave them a firehose of tweets milliseconds before everyone else.

There was an interesting case in the UK where a company that provided the audio feed for the Bank of England announcements fed the feed to hedge funds before everyone else heard it.

https://news.sky.com/story/bank-of-england-cuts-audio-feed-o...

Edit: this is my uneducated opinion not legal advice.