Your interpretation is not correct. The tern NET WEIGHT means the weight of the dangerous goods itself. For liquids, it means the net volume of the dangerous goods. No packaging material is included. This definition is spelled out in DGR Appendix A under NET QUANTITY.
With explosives, when the term NET WEIGHT is used, it means the weight of the explosive plus the weight of the container such as gunpowder and its cartridge. For pure explosive substances only, the terms NET EXPLOSIVE MASS (NEM), NET EXPLOSIVE QUANTITY (NEQ), NET EXPLOSIVE CONTENTS (NEC) or NET EXPLOSIVE WEIGHT (NEW) are used. They are synonyms. DGR Appendix A also carries these terms.