For those that don't know, grand juries declining an indictment is extremely rare. A grand jury is basically a check on prosecution, that they have to have some initial evidence before charging someone with a felony. The standards are much lower than the subsequent criminal proceedings.

The grand jury only hears from the prosecution, there is no defense involved. Only a majority of the grand jury has to sign off, not unanimous like in an actual trial. The standard of evidence is just probable cause, not beyond a reasonable doubt. The rules of evidence are relaxed, meaning hearsay and other evidence can potentially be introduced that would normally be barred from a trial.

Because of the above, the rate of indictment from a grand jury is very high, over 90%. Most prosecutors will go their entire careers without getting a "no true bill" (meaning the grand jury did not sign off on an indictment). There's a saying that "a grand jury would indict a ham sandwich." So the fact that there was no indictment here is a big deal. It will probably hurt that prosecutor's career.