True, it does not say the reason for the decline to indict. It could have as much to do with the overall decline in quality of the DoJ and its cases as a whole over the past year. Many nonsalient crimes will also go unprosecuted under this DoJ, but they will not generate headlines like this one.
The US DoJ does not prosecute in county courts.
From TFA: "A Clermont County grand jury, however, opted not to indict..."
It appears this prosecution was brought by local Ohio police; the federal Department of Justice would not have been involved in any way.