How and why the feds killed a talk on Tor-hacking at Black Hat

"The feds put the hammer down — most likely the National Security Agency. [...] “So with this, the researchers suddenly can’t talk about it because of a National Secrecy Order. [...] The source didn’t have first-hand knowledge of this incident but based their assessment on knowledge of the NSA’s operation and its background with Tor." (emphasis mine)

So, the author of the article doesn't actually know "how"...

"The NSA likely put the screws to CMU to back off, the former intelligence official said, and there are two probable reasons: either to protect its own use of Tor or to ensure that knowledge of how to crack Tor remains within a more limited circle. Tor and its variants are used by U.S. intelligence case officers operating in the field to communicate securely wherever they may be"

...or why, to any great degree of certainty at all.

Heck, almost anyone with some passing knowledge of the Snowden revelations could have guessed all of that. Yup, the talk was likely suppressed by the NSA, with some kind of court order meaning the researchers can't talk about it, either to protect a crack they're already using, or to stop others cracking their own use of it.

Or, have I missed something, and is there an actual story there?