Fred Rogers was a music composition major at Rollins College[1] and his wife Sara Joanne Byrd majored in piano[2]. So it is no wonder that he cared about the music on his TV show.
Some of his early work as a producer was also for the NBC Opera Theater and Firestone Hour TV shows, which broadcast great performances of classical music and (you guessed it) opera.
[1] <https://scholarship.rollins.edu/tomokan/67> page 69.
[2] <https://scholarship.rollins.edu/tomokan/66>