Resource Development Associates interview questions

I was contacted for a screening interview approximately 6 weeks after applying. The interview was pretty standard, and I was told that I would hear back within about a week about next steps. What I received was an email informing me that prior to interviewing me, the position had already been offered to another candidate and that individual had accepted the position. I'm questioning why I was asked to interview when they had already made an offer and were waiting for an answer from another candidate. I felt like my time (and theirs) was wasted.

I did two interviews and an exam (written + excel). In the first, they asked questions about my experience with qualitative/quantitative analysis, with consulting, my working style, and ability to handle deadlines. For the second they delved more into my consulting philosophy and management experience. In the end they offered me a job as a Resource Associate due to limited experience managing projects/teams.