As a musician, I can tell you sometimes these things can happen coincedently. Maybe he heard the song before, and 4 months later, he had inspiration for the prelude without even knowing it stemmed back to this song (and yes there are similarities, not in exact pitches of course, but more in general content). Maybe he never heard the song and it just happened. Maybe he found inspiration from the song directly.
None of those are "wrong". Many great artists have copied from each other. Creating music these days usually isn't about creating something entirely new, it's about a different take on things already out there. Even among your favorite artists, they will most likely have copied or found inspiration elsewhere.
Please note, using something for inspiration is different than just copying something. He didn't blatantly copy it, it is different enough to be his own work.