@JJ - I was trying to say it's NOT "a choir thing".
It's a Sam Lee "thing".
If you Google him in some other videos you might see more examples.

I thought I recalled Lucy Ward using odd arm gestures but actually I quite like her actions here
https://youtu.be/-CpEJ-8rV4s

I'd name others if I could find videos but TB I need clues.
It's difficult to discuss otherwise.