This doesn't actually prove what was stated earlier, which was "Indians develop abdominal fat more easily than others." What you quoted just says that Asian Indians in North India have more abdominal fat (the authors should've clarified what standard that was in contrast with). A population having more abdominal fat is not the same as it developing it more easily due to genetic factors. The same study you referenced says the following:
"Possible reasons for low LBM [less lean body mass] in Asian Indians remains unclear, and genetic susceptibility remains uninvestigated. Since Asian Indians have been exposed frequently to chronic protein deficiency due to exposure to famines, food shortage, and vegetarian food, it is likely that these factors may have affected the skeletal muscle mass."
It might be true, of course, that there's some genetic predisposition towards abdominal fat amongst ethnic Indian populations in contrast with other populations, but, what you quoted doesn't say that. And, it's normally pretty easy to find statistically significant differences between populations with regards to genetics, even when those differences are not significant in any other meaningful sense, and intra-group differences tend to also be a lot bigger than inter-group differences. Regardless of any of that though, we're looking at a population of over a billion here. To think that it's genetics limiting 1 billion people to 0 boxing world champions is very simple-minded. It's a developing nation with vast malnutrition that hasn't developed a culture of sport outside of hockey or cricket, which they do well at.
Yup, this is pretty obviously true. I think plenty of the Pakistani interest in the UK in boxing is because of Amir Khan, and I wouldn't be surprised if England could field a team of amateurs comprised solely of ethnic Pakistani boxers which was better than what the Pakistan Boxing Federation can field.
India's got a population about ten times that of the UK but about a third of the number of amateur boxers, and they're spread out over a huge area. There'll be hardly any boxing gyms outside of major cities, there won't be much funding for them because there's next to no interest in the sport there. The pro boxing scene in India is practically non-existent because there's no money in it. You don't get world class boxers when you don't have kids going to boxing gyms.