My experience of delivery drivers is that they get treated really badly by their employers. Most drivers ( apart from the Royal Mail)are self employed and their companies expect them to achieve the impossible, like delivering a large number of parcels in too large a area. So they end up rushing around like headless chickens, as they get paid per parcel or get fined for the one's they don't. It doesn't excuse the reason for throwing a parcel over the fence.
Glad you got your parcels.