Meta Software Engineer interview questions

I was contacted by a recruiter from San Francisco. After the initial chat, for the second round, a product manager from Seattle office contacted me to do the phone screen. He asked me a question related to sparse vector. I recommended and coded tree solutions including hashing, linked-list and array. Unfortunately, the interviewer was not very knowledgeable. I corrected him in regards to memory management and he made a wrong comment about Dictionary overhead. It is very hard to believe managers like him is able to work at Facebook. It is very unfair that he mentioned giving too many hints to me during the interview as an interview result. I feel very disappointed.