It can be any of those people, true. But EEOC also says; harassment is illegal when it is so frequent or severe that it creates a hostile or offensive work env

It can be any of those people, true. But EEOC also says; harassment is illegal when it is so frequent or severe that it creates a hostile or offensive work environment or when it results in an adverse employment decision (such as the victim being fired or demoted). So I think he is responding to the second half of that definition, meaning it's not totally irrelevant. For a client or customer's harassment to be illegal it would have to be "so frequent or severe it creates a hostile or offensive work environment". Note that "offensive work environment" certainly doesn't mean someone was offended once. Let me caveat this with I have read absolutely none of the accusations levied. I do think that sexual harassment should be defined carefully. In some cases what people are describing as sexual harassment is actually assault and I think the two should be carefully distinguished.