They contracted a specialize company to investigate, collect the facts and present their conclusions. The conclusions would be sent at the same time to the alleged victim, the HR and the manager.
In this case the conclusion was that there was no harassment according to legal definition. These argumented conclusions would have been presented to a trial as reference if any party would want to contest them.
The company performing the audit is specialized in it. So they can recognize a real harassment from an abusive claim. They also have no interest in the company. It is in the interest of the company to call them to get a leverage to apply whatever measure they would find appropriate. If the victim is an employee, and he/she would consider the reaction inappropriate and abusive, he/she could complain to a tribunal.
Today, a company that is not reacting like that (diligent an investigation by an independent party) to a harassment complain would be considered a priori suspect or would be consider to have failed complying to its duty because it is their responsibility to do so.