"Their own source" looks like they are bringing their own files or (more probably) their Spotify or YouTube. It happens all the time on public transport. Or did you mean bringing their own music and taking turns at sharing it with the other people around? That might be against the terms of service of some services.
Surely, since "silent disco" only really works if everyone is dancing to the same music (which is the only thing that would make sense for a post about synchronizing audio), they're using "source" to mean "device"
