Well, I figured out how to return on Match in the store menu. And I'm rescanning to see if it continues to upload the 5,000 songs it missed last time. Because it already successfully scanned my music earlier, all the 5,000 songs it missed this time are already in a dehighlited, light grey font on my iPhone, so I can directly see the songs that Match today decided weren't there in my iTunes. Is anyone having similar problems?
Sorry for a wasted post. I should have waited before posting this. I just needed to have Match rescan and it picked everything back up. I think it was an issue with the external hard drive (where my iTunes files is stored) being dismounted improperly by a lack of power (power cord was jiggled or something like that) and the dismount caused Match to misinterpret the correct content of my iTunes folder.