Muting players

So I was just told that if I mute someone, they can STILL see what I type? Is that true or false. I was under the impression they cannot see what I type if I mute them.

I was in a game, where my adc was not focusing the adc in fights, and getting us killed, and i asked him to please stop, and focus. He said it is his lane, and i should STFU, and he can do whatever he wants. So I muted him, and said in team chat that he keeps focusing support, and that is why we're dying, the guy logs out, afk's all game, causes us to lose.

They blamed me for it, all but 1 person, cause I went udyr support, which I have no problem doing, and we would have easily won every fight, if he focused adc, since i got him to 5-10% every time.

I just don't understand people, and so I supposedly get reported by 2 people, because I am trolling with Udyr support. I mean it's silver, anything works ;P Also, I don't troll, its legit, it works, i've done it many times. Does this happen frequently, that people are this toxic in this game?