Why wasn't I hired if job interviewer told me she needs workers?

I went to a job interview on Tuesday and met with a Human Resource lady. I have 3 years of warehouse experience at another company and it was the same type of business that I interviewed for. She told me that she don't have the power to hire me but that she really does need workers. She told me to call her if I didn't hear from her by Friday. It turned out that I received a letter in the mail Thursday saying thanks for coming but we chose other candidates. Since my background was good I felt I would get hired. Was there a good change I didn't do well in the job interview?