I think you are giving too much credit to these "peaceful protesters" there in LA. Of course their phones are on. How else are they going to live stream their peaceful protest on Facebook or TikTok?
I wouldn't be surprised if they were actually using the Zello app though. It was in heavy use during the Jan. 6 event in DC. After that, Zello removed the search option for finding channels. But if you know the channel name, or if someone is sharing the QR code there on the ground, it's easy for several thousands to be added to a channel.