Article 32 hearings are only similar to grand jury proceedings if you are a reporter trying to explain things you don’t really understand. They both determine whether there is sufficient grounds for a further trial (court martial in the case of the military) and an Article 32 hearing can result in punishment, unlike a grand jury outcome. However, article 32 hearings were always open to any member of the command in my 20 years in the Navy. Most people just had other obligations at the time they were held, or had no interest in the event. One summer, 30 or so of us Midshipmen on a training cruise were ordered to be at an Article 32 hearing as a training event. Not a very exclusive event.
While I am certainly no expert, I do not think an investigating officer, the official at a Art 32 hearing, can punish-only commanders can adjudicate non-judicial punishment, and only a courts-martial (with either soley a judge in summary proceedings or a jury in other types (genreal, specific BC etc) can convict of crime.
If they are allowed to be open, then fine, so what, if they are closed, same-same. I have been involved in a few as a commanding officer or as a witness, and I gave no thought as to whether it was open or closed. The people who needed to be there were so ordered or invited at government expense if not government/military members. Of course, they were not of the visibility this case is.
The outcome of this event will be that the investigating officer will recommend to the General C-M convening authority (commanding general of either FT Hood/III Corps or the next CG) to proceed with a genreal courts-martial.