Google Software Engineer - Internship interview questions

Got a interview through a referral. Got an email to schedule two phone interviews. Both interviews included an algorithmic question which I had to code in Google Docs as the interviewer observed. The second interview also included a non-coding question where the interviewer described a requirement and I had to describe how I would design and implement the system in scale.

2 technical interviews, then interview with the head of team. I passed the technical interviews, but the team manager, although seen my CV, said I lack experience and knowledge. I don't know why they summoned my at all\why the manager questioned the technical interviews I had.