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.
again as I understand it strictly speaking a foreigner should be casteless, and hence untouchable.
But that discussion implies that the actual behavior towards foreigners does not match that, which would seem reasonable to me. Indians will need to interact with foreigners, if they are without caste that would be a problem, so how to fit the foreign into the social system.