The "parties" of a treaty are governments. This has nothing to do with GPL. This is saying that a government can't say "you aren't allowed to sell software in the country of Frain as a non-Frainian unless you provide the source code for that product (whether to the end user or to the government)". They leave an exception for "critical infrastructure", because it was hard to argue that the government of Frain shouldn't be able to require that nuclear control software come with source code. Essentially, I don't see why this clause is concerning. It is clearly a form of pandering to the interests of software developers reliant on intellectual property rights, but only in a way that seems to me mostly about forcing capitalism on nation states that might disagree with its premise.