Good point. It's the EU trying to 'protect' us from foods that contain too much sodium, but doing it in an incorrect way and thus making it more confusing than helpful. A bit of background:
In chemistry, salt can be any compound of ions (non-H/O/OH). In fact, there are many salts in Jake, e.g. calcium citrate, dipotassium phosphate and sodium iodide. The thing is, not many people know these are salts, but almost everyone knows table salt. So in everyday speech, salt = sodium chloride.
But even when we accept this, it's still quite something to just say that salt = sodium x 2.5. The calculation comes from the molar mass of table salt: 58. Of which 35 is sodium and 23 is chloride. Which means that in every 250g table salt, there's 100g sodium. Great, but it simply doesn't work the other way around. There could be 0g chloride in a product and 100g sodium and the label would still mention 250g salt.
The objective is clear: we are eating too much sodium and the EU wants to help us eat less. The EU assumes that (1) people that consume excessive amounts of sodium read nutrition labels (2) do not understand what sodium is and (3) do understand that salt is table salt. This is what the EU labelling law says about the matter:
(37) Since one of the objectives pursued by this Regulation is to provide a basis to the final consumer for making informed choices, it is important to ensure in this respect that the final consumer easily understands the information provided on the labelling. Therefore it is appropriate to use on the labelling the term ‘salt’ instead of the corresponding term of the nutrient ‘sodium’.
We stand behind the goal of lowering our overall sodium consumption. But trying to accomplish that by providing misinformation based on stacked assumptions seems to be off.