> How can they have legal standing for such a claim, unless one of the authors had privileged access to Wolfram Research knowledge to misappropriate a trade secret?

The absence of legal standing obviously is something that can be raised once a lawsuit is underway, but it doesn't prevent the threat of a lawsuit, and many organizations will knuckle under to the threat of a lawsuit from a wealthy opponent just to avoid the expense of consulting with lawyers if there isn't a big cost in avoiding the lawsuit.