I could be mistaken but I thought they got their name from actually singing too? I believe the name for the “chorus” effect in audio recording comes from that experience - hearing the sound of a group of people singing instead of one person singing. Regardless, the name is appropriate.
Background dancers are often called a chorus:
https://en.wikipedia.org/wiki/Chorus_line
https://en.wikipedia.org/wiki/Ensemble_(musical_theatre)
I could be mistaken but I thought they got their name from actually singing too? I believe the name for the “chorus” effect in audio recording comes from that experience - hearing the sound of a group of people singing instead of one person singing. Regardless, the name is appropriate.