I think what may have happened is that they simply didn't clear these injections with the AFL first.
In this scenario, almost everyone could be telling the truth (well, mostly); it was "borderline" and "radical" treatment like Reimers said, but not necessarily illegal. But if they haven't covered their backsides properly by checking with the AFL, they may have skated a bit too close to the borderline for comfort.
That explains why this is even a "Story" in the first place. If they had official clearance from the AFL, they could just show the journos the documentation saying it was 100% legit and it would be a complete non-issue.
Now this would be ridiculous stupidity from the club, leaving themselves open to all this stuff because some idiot didn't make sure they were covered first. That explains the stone faces and worried looks at the press conference. But it's a long way from being a bunch of cheats.
Everything else about where Dank got his stuff has nothing directly to do with Essendon.