And millions of Indian non Hindus and people in neighbouring countries don't.

Curry is a global cuisine.

It may originate in India, but it has been incorporated into local cuisines all over the world. Most countries in Asia have their own versions of curry at this point. I'd argue that the UK does too, even if they call it "Indian". Even the concept of curry as a category of food is largely a British invention, and many of the things we've been calling curry for more than a hundred years have little relation to Indian food.

Also, India is a large and diverse country. Many Indians don't eat beef, but there are absolutely whole populations of Indians who eat beef curry regularly.