It's a straight up orchestral section, that sounds intentionally arranged in a very traditional way, as opposed to being unorthodox (there's the rest of the song for that). I feel like the whole point was to sound like a classic cinematic movie score, but the context of how it's used in the song is what makes it different.
Yes, I've heard orchestral scores arranged similarly before. And I've heard the Tchaikovsky piece that has a very similar melody to it. But they don't give me the same feeling as this does.
It's so beautiful, and makes me feel like I'm watching the finale of a classic 40s/50s movie. It evokes so much feeling, and that's what matters to me in music, not whether or not I've heard something sort of similar before.