Indeed!

Ahh, but that is not the same thing! The linked website demands to

Open interfaces and open software are two different things.

Other questionable points are the "publicly financed" and "developed for the public sector" parts. Is a purchase of MS Office by my local council a "publicly financed software"? It is certainly not "developed for the public sector", it is a general purpose product to be used by every Dick, Jane and her uncle.

Or is it only about the software developed exclusively for the council? In my parking system example, I, the developer and provider of such a system, may have initially written it for my local council and was paid with public money. But I will want to sell it to other town councils up and down the country, so it would not be developed exclusively for the one council. I may also want to sell it to companies, airports and other non-public organizations. So obviously I want to retain full rights to it. If I release it into the wild, what is to stop Johny from Kardashistan from copying it, changing a few lines and offering it to the council of Big Dogballshire for half the price?

My point about software being just another product stands. If my town council buys Coca Cola by truckloads to use at council meetings, it does not mean Coca Cola should give them the recipe. (Actually, in your world, it should give everyone the recipe because one council in one country pays for it with public money.)

As always, it helps to at least try to see it from the other side's point of view.