To me the theme of this passage is never trust strangers because you never know what they might be up to.Heres why.

  One reason is because  no one would be that nice unless they want something.In the passage, it stated that he offered her some stone soup.To me this is saying that he  needed some place to cook it so he offered her some.No one would ever steal or use me for anything because I dont talk to strangers.

  That is how I got the theme of the story.