Thank you very much for your detailed answer. I was already wondering about the mute button. But I find it difficult to guess the users intentions and wasn't sure where this would lead... Since I saw the comment pop up here, I thought maybe you know him/her and could tell me what his behavior is all about. Could well be, that I simply don't understand it as a German.
The flag issue is a bit confusing to me... I have found several comments and explanations, where users here say, its the same as downvoting...
I also see this little flag sign to the right of each post and am wondering if that is what you mean...