It is probably true that most Christians outside the Asian communities (note the plural) regard all South Asians as one undifferentiated mass, except when it comes to religion.
They forget that the subcontinent is home to over a billion people, in a landmass as big as Europe, and is as ethnically, culturally and religiously diverse as indigenous Europeans.
Also, there are special considerations concerning my community, the Punjabis. Our land was divided at Partition in 1947, with part going to Pakistan, comprising mainly Muslims and Christians, and the rest going to India, mainly consisting of Hindus and Sikhs, with some Christians. Needless to say, many Punjabi evangelical Christians in Britain are converts from Islam, Hinduism and Sikhism or come from nominal Christian families.