Funeral rites: why didn't it seem like the corpse was decomposing?

I think you have already guessed the answer. The climate and environment is so arid that he is,in fact, drying out, becoming a naturally-formed mummy. There is a 5000 year old Egyptian mummy called 'ginger' in the British Museum who was dried out and hence preserved by the hot sands around him; he is called ginger because he still retains a considerable amount of red hair (as well as scalp/skin.)