What the author called a 'rumpy' cat is the colloquial term used on the island, along with 'stubbin'. Otherwise the cat is called outside of the island, not surprisingly, a Manx cat. I've seen them scattered around the commonwealth as beloved pets, various tail sizes but probably sadly mutilated for cat shows for a more perfect rump. https://en.m.wikipedia.org/wiki/Manx_cat
if you've seen tailess cats in the UK (I know you refer to the wider commonwealth), they would not be mutilated, at least legally, like that. tail docking, ear docking, declawing, descenting (of ferrets), is illegal unless for the health of the animal or for a few working breeds where the dog is a working dog. (England and Wales do have some different laws on this than Scotland and NI)
https://news.ycombinator.com/item?id=20506954
Though I believe that it wasn't actually signed/ratified by the UK:
https://www.coe.int/en/web/conventions/full-list/-/conventio...