Just a verbal account, or any link to a news story?
Do we have a shootout, a gunfight between your source and the would-be robbers?
Nothing wrong with being "careful," however . . . some skepticism rises when I hear an unsubstantiated "Armed Citizen" story from a stranger . . .
Again, being careful's a wise policy, and deadly force is legal to prevent death or serious injury to the innocent, but . . . the INNOCENT don't always WIN gunfights; being careful is NOT totally equivalent to arming oneself.
Just as an aside, I thought the Chicago area had severe anti-gun laws in force, at least, for law-abiding citizens.