They’re not wrong in saying that that’s the law. Maybe as you say it’s not law in traditional sense but the requirements are quite clear.
> You may register a .eu, .ею or .ευ domain name if you fulfil the following criteria:
> You represent an organisation established in one of the European Union Member States; or Iceland, Liechtenstein or Norway.
You are an individual residing in one of the European Union Member States, Iceland, Liechtenstein, or Norway, or a citizen of one of the European Union Member States, Iceland, Liechtenstein, or Norway (as of 2 August 2021).
> You may register a .eu, .ею or .ευ domain name if you fulfil the following criteria:
> You represent an organisation established in one of the European Union Member States; or Iceland, Liechtenstein or Norway. You are an individual residing in one of the European Union Member States, Iceland, Liechtenstein, or Norway, or a citizen of one of the European Union Member States, Iceland, Liechtenstein, or Norway (as of 2 August 2021).