Yeah most of us know the Fairlies are in Wales but just like Europeans took to calling the United States "America" in spite of America consisting of dozens of countries on two continents, we Yanks often call the entire UK "England."
As for its pulling power though, the recent article in the 3rd Quarter 2020 Prospector has an official report written in 1875 that the Mountaineer could pull 12 loaded freight cars over Veta Pass whereas the next largest locomotives could only handle eight loaded cars. Playing it safe with a replica and running only six passenger cars still provides plenty of space for passengers. The real problem was maintenance - and a series of manufacturer defects that would have to be addressed for it to run properly, if you can get past justifying the ratio of cost vs. return.