Sure, I don't mean that it was evidence at the time, rather that suspicions held by the advisor seem to have been proved true. I presume that advisor felt just

Sure, I don't mean that it was evidence at the time, rather that suspicions held by the advisor seem to have been proved true. I presume that advisor felt justified in warning others that the author might be a problematic hire, and a scandal like this is evidence that the suspicion was correct. I think the right question to ask is whether an advisor is obligated to give positive recommendations for an advisee if they come to regret having taken them on. My sense is that the advisor was correct to notice that socially something was "off" about the author, and correct that others might regret hiring her, just as he(?) had come to regret choosing her as a student. I don't know though whether it's legal under current EU law to act on these observations and experiences.