You may have seen this ad in the career site, the company website, an ad in the magazine / newspaper, or the company’s ads. An acquaintance in the company may also have informed you.
According to your answer, the HR specialist will try to get more clear information about you. The main purpose is to learn if you know someone in the organization. Someone from the institution you are applying for may have provided information. If this is the case, you should definitely mention it during the interview questions.
Because it shows that there is someone in the company that trusts you. This means you have a reference. If the interview is good, it will provide a source of information about you. This will put you a few steps ahead of other candidates. This is called networking in the business world.