I agree with this. I was asked to send additional application materials AFTER I received the interview invite. I don't think there is a rhyme or reason to it. It is more likely that this particular admin process runs in parallel with the admissions board's decision process. I received confirmation that my application was complete only last week, three weeks after the original invite.
Another DP: Last week I received an email from Ross asking for one of my diplomas, and the next day I received an interview invite - before I sent the requested document.
Bottom line, hard as it is I would refrain from reading too much into the timing of others' experiences. Just try to be patient for the published deadlines.