No, they originate from the same idea, but they’re definitely different movies
Corbucci used the idea too for Minnesota Clay, he was fascinated by this idea of the loner, a sort of wandering samurai, but turned it into a much darker vision in Django.
It’s hard to invent something really new, something completely original. Look at the great writers in history: Sophocles, Shakespeare, Dostojevski - they often used trite (or even existing) storilines, but turned them into something that people had never experienced before. Both Fistful and Django were such movies: they weren’t original, still they were like no film had ever been.