The conclusion happens to be correct but the argument looks invalid to me. A man can smash a clock or a compass just as easily, but that doesn't prove that these defenseless devices cannot provide useful information.
The real argument may have went something like this: "I am a very busy and violent man, who, as I have just demonstrated, is quite accurate with a deadly projectile weapon. In light of this, would you perhaps prefer to rethink your policy of holding up my entire army ?"
Here's the new thread for posting quotes, with the usual rules: