George martin did write a few piano and orchestral bits here. He was a great addition musically as well as sonically. But he certainly did not write the music. There are quite a few books out there if you want to better understand what happened. Geoff Emerick’s book is very informative. He was the recordig engineer.
Paul is a great musician because he can get in the zone, stay there for quite a while, then remember what he did while he was there and finally write it all down.