I'm not seeing any interpretation being done here, but judge for yourself. Here is what the GDPR actually says (Art. 37 Designation of the data protection officer):
> (1) The controller and the processor shall designate a data protection officer in any case where:
> a) the processing is carried out by a public authority or body, except for courts acting in their judicial capacity;
> b) the core activities of the controller or the processor consist of processing operations which, by virtue of their nature, their scope and/or their purposes, require regular and systematic monitoring of data subjects on a large scale; or
> c) the core activities of the controller or the processor consist of processing on a large scale of special categories of data pursuant to Article 9 or personal data relating to criminal convictions and offences referred to in Article 10.
That's the UK's straight-forward unequivocal explanation of the rules. Where there is room for interpretation or uncertainty, the ICO is very good at pointing this out. It doesn't here.
As poisan42 points out - it echoes the words in the actual article, directly.
The GDPR replaces the 1995 Data Protection Directive.[4] Because the GDPR is a regulation, not a directive, it does not require national governments to pass any enabling legislation and is directly binding and applicable.[5]
Only for the sake of correctness/completeness: GDPR does allow member states to adjust certain details to bring them in line with local regulations (see Chapter 9). These are explicit opening clauses though that must not basically weaken or augment GDPR.
It's an EU Regulation, which under EU law the local courts have a duty to enforce. Local courts and laws will be dealing with all the details unless a case is appealed to ECJ.
To say that local courts and laws will have no influence is complete rubbish.
I suppose it depends where in Europe he would like to visit