This is literally one of the worst moves Twitter could have made to combat Threads or any of their copies. They're literally giving more eyes and coverage to Threads and painting them as a real contender.
- Limiting access to Twitter.
- Tweeting incessantly about the Threads launch.
- Threatening to sue Meta.
Musk can't stay out of the limelight, for better or worse, and in this case it is definitely for the worse. Threads would have had a tiny fraction of the hype it does had it not been for his antics these last few weeks.
Meanwhile (as the article says) Meta has confirmed no employee on the Threads team came from Twitter. So the letter is already shown to be completely without basis.