This professor was being accused of sexually harassing women, and these real women who were very upset to find out that @Sciencing_Bi, who was trying to join in their cases, was not a real person.
I can see why this in particular upset people. Through the lens of consequentialism especially one can see how unethical this is. Fake allegations delegitimize real people coming out against abusers. This is not just a harmless lie, this has negative consequences