Has anyone checked the scientist's social media? Border agencies are known to monitor social media. If he did something like, say, express sympathy for Luigi Mangione or Tesla vandals, this would definitely dovetail with a "terrorism" rejection.
The FBI defines terrorism as: "Violent, criminal acts committed by individuals and/or groups to further ideological goals stemming from domestic influences, such as those of a political, religious, social, racial, or environmental nature."
Clearly, criminal trespass on someone's Tesla to discourage Elon Musk from taking actions against your ideological goals falls within that category.