This is just the indictment, but that wording does mean he forced it. That's the crime the indictment is referring to. It states he "ensured" participation, which means he made the event happen.
Not unlike what Cosby did. We are beyond "loosened inhibitions" at this stage, this about the girls losing control or even passing out, or going in and out of consiousness.
Again, like Cosby did.
It's possible, if not likely, that some weren't even aware they were being given some drugs, whether they took some on their own or not.
The grand jury was probably shown evidence of some kind but drugging girls for the purpose of keeping them there, or for the purposes of assault, would be a crime.