I think this article is at least somewhat factually wrong. Yes Facebook admitted an error in their code. I suspect that was related to how the various groups were suspended not the child porn directly.

It still looks like somebody planted all the porn on those sites. That was not a facebook bug according to anything I have read. It may have been at least partially attributed to the Casey Champagne that the DailyBeast article refers to. Most likely it was put there by some really creepy Hillary supporter. Frankly I wouldn’t want to be in their shoes if some of the porn was indeed child-porn. Possessing anything like that is enough to be arrested over.