Whether their lawsuit is valid or winnable is not part of my point.
But anybody can sue anybody, anytime. And they do it all the time.
Right, but there’s also something called filing frivolous lawsuit for which the lawyers are penalized big bucks. If there’s no causation, as here, then a lawyer would be stupid to take the case. There has to be some attenuated negligence which requires duty, breach, causation, and damage. If the defendant lacks one of those elements you don’t have negligence.