The explosion looks to me like an air burst artillery round. This being the case and you can identify the trajectory (and therefore the direction to the firing point) from the shape of the cloud. It looks to me like the round was fired from a position some way along a line running about 2 o'clock from the tank hull. This, the relative size of the burst and the direction of the turret indicates that the tank may not have fired the round. As to the size of the burst, unless the picture has been altered, it is hard to think what sort of munition caused it, the burst from 155mm HE is much less impressive.