I wouldn't be surprised if Elon considers it just. Most people consider it just that a revolutionary technology owner is being held liable for their actions, even if they are nearly a decade afterwards.
Regulation for big corporations are more like suggestions these days, so this may even feel "fair enough" for Elon in retrospect.
Or the tweet was bullshit, and Tesla will do what every company does and determine whether it is better to settle or not based on the financial cost/benefit and not the truth or validity of the claim.