Was rejected for a job I didn't really want, so why am I upset?

I applied for a medical administration job, it was ok, paid great but it was a casual position and I would prefer something full-time.

They liked my resume, my selection criteria answers and I had an interview. I thought the interview went ok, there were some tough questions they asked that threw me but I feel I gave the answers they were looking for. At the end of the interview, they got my ID and got some forms for me to fill in.

I hadn't heard back so I went onto the job listing page and saw that the status had been changed to 'Position Filled'. I'm confused why I never heard back but I don't know why I feel so upset about it. I have experience in the position and feel like I could have been a good fit

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