Wilhousky and the "Carol of the Bells"
Among the audience at the first concerts of the Ukrainian National Chorus in New York City was a 20-year-old student at the Damrosch Institute of Musical Arts (which later became the Juilliard School) named Peter Wilhousky (Petro Vil'khovs'kyi). He had been born in Passaic, NJ to a Rusyn family originally from the Presov region of Slovakia. He was intrigued enough by the Leontovych setting of Shchedryk that by the 1930s he had created the now all-too-familiar English lyrics, which he copyrighted.
Why bells? It may have been that the melody and arrangment reminded Wilhousky of bells, or he may have conflated Shchedryk with another carols setting that may have been in the Chorus' repertoire, namely "A v Ierusalymi Dzvony Zadzvonyly" ("O in Jerusalem the Bells Rang Out"), where the choir literally imitates the sound of church bells.
Wilhousky would go on to become an influential choral director and teacher, as well as arranger for Arturo Toscanini's NBC Symphony, and as such had ample opportunity to popularize his new English text.
The rest, as they say, is history.