(My replies are asterisked)

The fact that the operator calls it a halt? 

* The name is irrelevant to defining an object, it could be named 'Joe Bloggs'. Naming it 'halt' doesn't define what a halt is. 

It's a common pattern on preserved railways to distinguish between "full service" stations catering to tourists (i.e. with a car park) and "only a halt" where the only expected customers are walkers.

* "With a car park". See? Yet another subjective, personal interpretation of the meaning of the word 'halt'. Classifying all railway stations as 'railway=station' & adding fact-based sub tags, such as 'usage=tourism' & 'request_stop=yes' etc. removes ambiguity, making the OSM database more accurate.

But frankly, the definition of a halt is beside the point.

* No it's not. The very basis of OSM is how objects are defined. The whole wiki is a list of definitions. That 'halt' is provably subjective sits badly within OSM.

My irritation is with overriding the work done by local mappers based on individual opinion.

* It was undertaken after discussion on Talk-Gb
https://lists.openstreetmap.org/pipermail/talk-gb/2020-January/024096.html
https://lists.openstreetmap.org/pipermail/talk-gb/2020-February/thread.html#24097

* Some concurred, some gave additional details, no one objected. 

* Changing them from station to halt was performed unilaterally, overriding the work performed by contributors. 

It doesn't sit well with a collaborative project.

* It was a collaboration.

* I note the Wikipedia pages describe them as 'railway stations'