The article itself says that there are multiple meanings of "character". One of which refers to a persons reputation and can be traced back to "the Greek charassein, meaning “to sharpen, cut in furrows, or engrave.”
So perhaps this is convergent evolution? "Character" can also mean symbol, like a key on a typewriter. That would make more sense as a descendant from "engraving".
I'd hazard a guess it's that multiple words which sounded vaguely similar were merged into the most dominant form as a result of people being too lazy to differentiate them by minor nuances of pronunciation.