"Unknowingly lied" isn't really lying is it? And I don't expect her personal staff to be flawless and having worked in IT trying to piece together things that happened even a year ago, I can easily see how something may be overlooked, like a single email chain.
Looking at this from a tech perspective, I don't think they find that one chain and still have reams of email to go through. That's what they found. If they were still digging through the recovered emails, why would they release that bit of info? Political leak maybe, but I don't think the Justice Department has it in for Hilary specifically.
People up in arms about this seem to miss the obvious political angle, probably intentionally. There was no instance that led to this probe, no Bengazi, no accusation. The initial probe came up because she was called out for doing what was standard practice. Once that angle was tapped out, FOIA requests we're made to see if maybe she broke the rules somehow. Now that that is tapped out (the supposed 4 classified emails which weren't classified when they hit her server) we're looking for mistakes and inconsistencies. If that gets tapped out, people can always play the angle of how she reacted personally as some character flaw.
It's the equivalent of a nuisance audit by the IRS. Legal, but clearly politically motivated. Given the two decades that people have been trying to get dirt on her and comfy up empty, trying to smear her suggesting she had a friend killed, that she was responsible for an ambassador dying etc, I'm not all that surprised if she doesn't handle this all that gracefully.