He is the bishop with responsibility for parishes that don't want women priests in London and tbh they are all very high church so he wouldn't be used to this sort of music.
The church is hired out as a concert venue all the time - I've sung there - and there is usually a pretty strict deadline on being out which I think is 9.30 so he had probably given them a bit of leeway.
IIRC the vicarage is abutted onto the back of the church - there was a maze of rooms behind some of which looked quite residential, in which case it was going on in the same building as his house.
Not perhaps the best way to approach it though.