Ok that one's easy, the wisher wasn't a very nice guy.

The traditional image of a djinn wouldn't have reacted in that way, they don't care about morals, usually. They are unknowable entities (sometimes called demons or devils or lesser gods depending on the specific myth) bound to grant the letter of any request made to them by a human in possession of their prison. They don't care about human morals or codes, and mostly will just try to find any way to subvert your desire while remaining true to their binding.