Mustard grows naturally in warmer areas like the Mediterrenean and Mid East, so we must have named it first. thats like asking why do we call a horse asb...
Exactly the point. If you notice with all other words that use `khar` as a prefix, the word itself embeds the meaning of the word: khar, but not in the case of khardal or kharbozeh. Just think of all the words that start with khar!
. We are older civilazation so we must have found it and named it first 
