The story in that comment does sound consistent with behaviour at similar rallies, though. When there was that protest outside the Melbourne military expo last year, random people just walking past were being assaulted because they looked like attendees (committed the crime of wearing a suit). It's also worth noting that nothing in that linked Facebook statement actually disproves the anecdote you shared:

So what we have here is a noisy but strictly non-violent footpath protest, that didn’t block roads, driveways or building entrances, during which even the Queensland Police (who love creating bullshit excuses for arresting activists) couldn’t find ANY examples of assault, hate speech, trespass or anything else for which they might justify arresting someone.