The B737-400 when flying empty needs ballast in the rear hold to achieve balance, about 400kg. So with a light load it must be loaded from the rear. Usually putting all the bags in the back will do it, but perhaps there were not enough.
Aircraft are all different. The B737-200 had no probs at all. The B757 never has a problem. Our B767-300 sometimes have to limit freight in the fwd hold to get CG in limits, and always have to seat the pax further back. MD80 and F100 are a nightmare. Sometimes tail heavy and sometimes nose heavy.