The claim that halal restaurants have an "almost religious following" among non-Muslims raises my eyebrows almost as much as the claims that e.g. there are "no-go areas" in Muslim parts of Birmingham.
I've lived in various parts of the UK all my life, I've been involved in Muslim communities and I've been to a lot of restaurants, both halal and otherwise. Basically the only reason a restaurant will advertise its halal status is to indicate this fact to Muslims. It might be the case that e.g. Lebanese or Indian cuisine is popular among non-Muslim Brits, but that's because of the taste of the food. If anything, there are ethical concerns about halal meat in my peer groups due to the controversies over stunning, and undercover videos showing cruelty in some halal slaughterhouses.
Honestly, the first paragraph reads to me like a string of inflated claims that's been shivved in there to exaggerate the significance of the article's content.
Umm.. Majority of indians are hindus not muslims.
I wouldn’t say that that’s the only reason either. Even if a non-Muslim Indian does set up an Indian restaurant, they have a high chance of attracting recurring customers that happen to be Muslims that observe a keeping a halal diet.
Edit: fix typo