"He didn't literally say "The US is safer because of 9/11", but he did make the comments that post-9/11 terrorism is all about scale, and that it's harder to pull off a large scale terrorist act because of the threat of being caught."
So, in other words, you see that the problem is that the words "The US is safer because of 9/11" most straightforwardly imply that 9/11 directly made the US safer, whereas the reality is that 9/11 only indirectly made the US safer.
What the idiot paraphrasing Schneier should've said was that "The US is safer because of the response to 9/11."