I'm not sure they told the other girl what to wear, and just because they wanted me to wear semi casual business attire doesn't mean they needed to wear it as well. I was a little surprised and felt a bit overdressed, but overdressed is better than underdressed.
I looked it up:
http://www.ehow.com/video_12219167_d...sual-work.html
According to this jeans are okay for semi casual, just FYI.