Correct me if I'm wrong, but I think it has something to do with the CBA players are under. "Technically" they're on their break, and "technically" they're not supposed to be training in their "official" facilities where they are employed, that is, the ETAF, with official club personnel.
www.afl.com.au/news/510960/return-to-tra...aled-for-afl-players
That a bunch of players got together to train - on their own time, since they're always under pressure to return in great, not good, but great nick - is not remarkable. I'm certain heaps and heaps of players do this. The fact that it was filmed and broadcast is unusual.