I just got hit in the face with a sledge hammer

Sometimes before Christmas, I responded to an ad from a large NY law firm. Christmas Eve, I received a call asking to schedule a phone interview. Due to the holidays, I wasn't able to get in touch with the HR person for a few days. When I finally did, the phone interview was scheduled for today at 11:30am with an HR person and the HR Manager. During all this time, I did extensive research into the firm. I prepared Q&As that might come up during the interview. I had questions that I wanted to ask to determine if I'm a good fit. In short, I was prepared. This firm, and the position, are exactly what I've been looking for. The work, the people, the global reach--all very attractive to me at this point in my career. So, I received a call a few minutes shy of 11:30am this morning. The HR person said they were running a little behind, and that they'll call me back shortly. After about 20 minutes, I received their call. I was ready, with my game face on. We exchanged some pleasantries, then it hit. The HR Manager told me that they were looking for a Midlevel Associate, i.e. someone with at least 3 years experience supervising other attorneys. WHAT?!?!?! How could this possibly happen? I made it abundantly clear in my cover letter that I was applying for a Junior Associate position. My resume clearly states that I was a recent graduate, and there is no prior work experience as an Associate. The HR Manager went on to say what a great resume I have, what impressive experience, etc. and that she would consider me for a Junior Associate position had there been any opening. But, even though I have a few years of professional experience, they were not relevant to the position they're interviewing for. She wished me luck and invited me to apply back after I have gained a few years of experience. After the call, I took a few minutes to digest what had just happened. I called back the HR person and left a message, asking him to give me a call so I can clear up a few questions in my mind. He hasn't called me yet. I'm not mad or bitter about the situation. I'm just trying to understand what could possibly went wrong. Was I wrongly selected in the beginning? Or they had a discussion prior to the interview and changed their mind? Now, I'm sitting here, still perplexed as to what had transpired. So, what say ye, the collective wisdom of the Steez? (Oops, I posted this in the wrong forum. Would a mod please move to General Chat, some other appropriate forum? Thanks.)

I was, figuratively speaking.

Dude, is reading comprehension your weak point?

If I had a sledge hammer here, I might even do it myself.