I think one of two things happened. The first is TechCrunch simply didn't screen the hacks being presented in any way before they went up on stage. The second is they did screen them, but whoever did the screening had no problem with the two problematic submissions.

It's pretty clear to me the latter was has occurred, for a number of reasons. Firstly, the language in the apology refers to a failure to "properly screen", rather than screen. Secondly, TechCrunch originally tweeted a link to one of the two hacks in question (subsequently deleted). And finally, it's a high profile event being broadcast live. You're screening the presentations if only to avoid potential legal and liability problems.

And it's because of this that I have a hard job taking TechCrunch seriously when they say "we've worked hard to counteract it in our coverage and in our own hiring". It only takes one or two incidents like this to totally undermine any credibility you might have.