yeah, it sucked to get rejected so quickly. you're right, it may be more common than we see here. Thanks, and good luck to you too.
Hmmm... no. the only thing I can think of is if they do a more thorough computerized screen after secondaries. Maybe the first screen is for MCAT and/or GPA and the second screen is for a higher cutoff or a combination of the MCAT and GPA. I can only speak for myself, but I have more than enough research, clinical, volunteer, and work experience. I have enough leadership experience too, and I think being URM would positively affect my application. MCAT was on par w/ the school average but my GPA was definitely on the low end though (although if they had bothered to read my secondary, my low GPA would have been addressed).
So in total, it was either a 2nd round of computerized screening w/ a higher cutoff, or something like you said about the reviewer. I have half a mind to email them and ask them for feedback but I wouldn't know exactly what to ask ("can you explain to me why/how you decided I'm not worthy of your school in 23 hours?" doesn't seem like a good question).
Good luck on your apps.