It's quite possible that the musical skills you picked up from your piano lessons are reason why you had the "talent" to picked for your schools chorus.
My main struggles with piano were chords, and sightreading. Chords aren't really relevant in vocals since a single person can only sing a single note at any given time, and I wasn't great at sightreading then either. And I find breath control a lot easier than trying to anticipate where my hands need to go (as someone with small hands, a lot of pieces were quite difficult)
There was a similar screening process for the ability to swim, though it was actually for selecting those who could not and teaching them.