They are using this word ‘intent’ deliberately to remind us of the Clinton email decision Comey made. I don’t think ‘intent’ is the real reason they declined prosecution. I think it is more to do with the fact that 1) these memos were classified after the fact and 2) that he shared them with his lawyer (making it privileged in some ways, even though this ‘lawyer’ was really a friend he used to leak the memos) — and while these and other arguments may be irrelevant to the statute, it does make the prosecution of the case more difficult.
And if they suspect they will be filing other charges, they can always resurrect this issue or feel justice will be adequately served with a more solid case to prosecute. Why bring a weak case into a strong one?
I also heard that the one(s) classified after the fact were only classified Confidential.