It's different because he did not take the sheet music. He heard the recording and decided to play his own version of it. Music may well be the worst example here, because it happens all the time. Now I'm not sure with regards to the financial side of performing a cover (rather than recording it), but at least in a casual context it happens for free.
I think there's actually a surprisingly good analogy to music here: those "play X on the guitar" tutorials. The original artist plays the song, someone else hears it, figures out how to play it by ear, then offers to teach it (probably their own version/interpretation of the song) for free. Similarly, the OP saw a design, figured out how to code it up himself, and decided to share it with the world.
