(an unnecessary but fun) Fact: "Тихий" in Hindi (तीखी) would mean spicy/sharp (for feminine words)!
...so, человек can only be translated as "man"? I thought it was okay to translate it as "guy", oops
I think it is because "silent" is more like "mute" than "quiet". Silent would imply that he does not talk, whereas quiet would imply his tone of voice. Or that the amount of talking he does is minimal.