ZyLAB .NET Software Engineer interview questions

First interview have been made with recruiter agency via Skype. Second interview was with CTO of the company. They shared technical assignment to me. The assignment was quite difficult than an average assignment. By hard working around 10 day I completed technical assignment. Technical team liked it and invited me to talk further details about assignment, why did you choice it, how did you decide it etc.. Thirth inverview has been made with technical team, they asked some advance questions about data structure, algorithm, threads etc.. In my opinion they didnt focus most concept of the software development. Finaly, they decide I am not a good fit for the position.