"Scared of public channels" often means "doesn't have the psychological safety to say something out loud that might end up being perceived negatively or as though they don't know what they're doing."
I'm active on a programming language Slack space, what sometimes happens is that people are DMed directly with a generic / open question that dozens of others could also answer.
I know for a fact that anonymity can be used to encourage diversity of thought and honesty on public channels - this is the feedback I get from customers of a service I run (https://AnonymityBot.com).