I didn’t see it this year but I remember the music from previous years being very moving. Gets you into the spirit of the day. Music in the 3 weeks is only assur if it live or gets you to dance, although many of us are machmir and won’t listen to any music during the 3 weeks there are poskim who even mattir any acapela or recorded music so certainly moving acapela should be fine in this situation. Like kapusta said, I assume they asked a shaila.
