We periodically receive updates to that list [of malevolent sites] and received one such update to release on the site this morning. Unfortunately (and here's the human error), the URL of '/' was mistakenly checked in as a value to the file and '/' expands to all URLs.This sort of thing happens because of bad processes. It doesn't matter how smart folks are, if they work in a bad way, poor results will ensue.
Of course, I don't know exactly what occurred, but I'll bet you a pound that one lone double-super-genius is left to make changes to this file by themselves.
Update: Jonathan Wolter raises some questions about testing such changes.