If a user marks his/her profile as private, that is what one would see if one clicked on the user’s avatar. That notice is expected.
As for muting a user, one way to go is for the user to go to their preferences and enter the user-in-question’s username in the Muted Users box… and click Save at the bottom.
I know there is another to mute someone, but I’m using my wife’s iPad at the moment and I haven’t figured out how to switch between tabs without losing my place (such as back to this editor). My laptop HHD had a sudden catastrophic failure the other day. New laptop to be here on Thursday. In the mean time, I’ll go back to my forum and check it out. I’ll return here with what I find out - if someone doesn’t beat me to it.
Edit: Have the user go to his/her preference, then click Users. A button is there to add a user to the Ignore list. Press the button and in the box They enter the username they want ignored or muted, then press Save Changes.