It uses the MD5 of the image, no surprise there that there were collisions with ordinary files. I've run into MD5 hash collisions causing mayhem several times in my life (usually between unrelated email addresses, IIRC).
If I had to guess, you might have been hitting collisions in a truncated MD5 hash. It's not uncommon to do something like take only the first 64 bits of the hash. Doing this you are quite vulnerable to birthday problem issues.
I have no idea if the database is still somewhere, if so, we can look at the git commit and figure out what the possible UPCs are and narrow it down to a couple of hours worth of time stamps. I have a feeling it would probably be more than 512 bits though. UPCs are can be longish, plus a time stamp with each digit being a byte…
I highly doubt the database exists in any meaningful way though, since the product was shut down years ago.