The rules are clear - kick the ball away intentionally, to stall the play after the ref blows his whistle = yellow card.
However, could he hear the ref and or see the linesman? If he could either, the red card is justified, if he couldn't, he really shouldn't have been sent off. Do you think he could hear the whistle or was looking at the ref?
vid here: http://onside.dk/fodbold-video/champions-league/barca-arsenal-3-1-se-rodt-kort-og-straffespark