Yes, usually replies to a public post, are also public.

You might want to take a look at https://github.com/e14n/pump.io/wiki/Clients and https://github.com/e14n/pump.io/wiki/FAQ

Also, not to spam you (since this next link is partially mine), but these tips might help http://communicationfreedom.wordpress.com/2014/03/17/pump-io-tips/