People are not muted just because someone reports them. Reports are reviewed by moderators or staff and mutings are only issued after the review. Moderators can't close accounts but can make recommendations to staff for a closure.
I think it is likely that you received the warning after a moderator reviewed some of your forum posts, which I have seen being reported and I can see are somewhat controversial. Many people do not appreciate sarcasm or satire.
I was reported for supposedly being rude to someone in chat during a game. Which is sort of strange since I not only do not chat during games, but have chat muted in settings. Chess.com sent me a rude and aggressive warning and even saying something about complaints from several opponents. I only made my account 2 days ago. No in-game chatting. Zero. I Googled this only to find it is a very common problem on chess.com and some people have had their accounts muted, based on false allegations of a sore loser. Seems like anybody can say anything and not even have to provide screenshots as proof. Very sad place. I'm out.