I read/understand that it was the NYPD that was investigating Weiner’s sex crimes, and when they examined the devices, they found many emails, some of which indicate conspiracy to obstruct justice. The NY cops called the FBI which decided they could no longer hide the truth. Comey’s hand was forced by the fact that NYPD knew all about it.
It is certainly possible that since the NYPD was not signatory to Coney’s non-disclosure stuff, Comey had a problem.