Diagonal line joining intrument staff with voice staff

Can someone make sense of this? The piece is for voice and bayan (button accordion). At the end of the piece there is a line joining notes from the left hand to the notes of the choir - what does this mean? It can't be the usual piano notation for playing with left or right hands. The resolution of the original does not make it clear whether it is a straight line or a wavy one (like in a glissando).