Where I work, if something was considered confidential even if it wasn't something legally require to be kept secret, those who wanted it kept secret would call it a "leak."
Those who spread confidential information would, of course, be on the side of the people. (Until it was something they wanted to be kept confidential.)
I'd probably call what Comey did a leak. Not every word we use has to be defined by the legislature. Some have multiple meanings, and in many cases how one group of people use a word can be a little different from how the Great Decider of All Definitions views it. In other words, in common use words can be a bit squishy and good will and cooperation is required for communication; where you get scrupulous, exacting, one-true-meaning definitions is often are where there is no cooperation assumed: Contracts, courtrooms, legal situations.
The US used to be the most litigious country on Earth. We've popularized that to nearly every social setting, at least that doesn't involve boundaries. Not good. It makes language into a means of non-communication.