I think the more likely explanation is a player telling a joke or something like that to kick off the session. I know that Richmond do, or used to, do this before a game as a tension reliever.
If that’s what it was it was very tame.
whenever you see one of those selection announcement videos from Training on social media all the players are jumping on top of the player, ruffling his hair and whooping it up. That did not appear to happen here so I doubt that anyone is debuting.
I could of course be wrong.