In other words, the quote is completely bogus.
Caste system, on the surface, seems like hereditary fixing of labor roles. If applied universally, it should be easy to accept a member of a strong foreign army, or any army as a Kshatriya. So it makes no sense for every Englishman to assume a high caste, irrespective of profession.
But then, many “castes” are also, basically regional/ethnicities. In short, the rules which apply caste, are not uniform in any way and I would rather ridicule such an exercise than aid it.
A foreigner doesn’t need to have a caste, even if they wish to convert to Hinduism, when our argument is that we need to abolish caste in India in the first place.