I understand what your saying however, it makes sense that someone picking up a floating carcass of a dead fish would not need to snag the fish with a rod and reel, or use a net net of any sort to obtain it. It is very easily done with your hands. Or who is to say it wasn't obtained from the shoreline, or the carcass was obtained from a previous year and frozen to be used at a later date. None of these would be considered angling and thus not illegal.
Nothing in the freshwater fishing regulations indicates you cannot utilise a dead partially decaying fish as bait, if obtained in a legal manner despite there not being an opening for that species. If it is left to interpretation, only one can assume common sense would prevail. If questioned by a fisheries officer and they provide accurate answers to the questions there wouldn't be an issue. At no time have any laws been broken.
Some of the statement made have been very much misleadling. Ultimately, individuals who plan on fishing sturgeon need to educated themselves and understand all the legalities of what they are doing. The responsibility is theirs to know the answers if being questioned by fisheries officers.
Good luck!