I feel for the guy, making a living off of art is difficult. However, with an extensive email chain explaining the story was written as the ending of Minecraft, even going into detail about how it was to be displayed in game, an agreed upon offer (if a bit vague), and then an exchange of funds - with no immediate attempt to return said funds. I'm no lawyer, but that sounds a lot like a legally binding agreement. > So…
For what it's worth, this often comes as a surprise even to many German creators who are not aware of this because intuitively if you get paid to create something "for" someone, you sell them your rights to it. But in reality that requires an explicit contract spelling this out. A typical example is professional photographers actually only selling you prints of the photos they take for you, or a design agency not giving you the source files for designs they create for you.