Also "Eleven protesters were arrested on suspicion" is a pretty low percentage of incidents for a 2 million or so strong protest. That to me sounds like pretty good evidence that it's largely very peaceful.
Cracking down on a massive popular protest against overreach would just be counter productive to Chinese interests. My guess is that these eleven are not just random protesters, but were either identified as leaders or will be used to send a message.
They were arrested for last week's protest of approx. 1m people, not Sunday's. According to some estimates, the police injured 70+ people and arrested 11.
It's pretty shocking for us HKers, as the police used to be trusted and looked upon very favorably. That trust has deteriorated since the Umbrella Revolution.