Indians are highly selected yes, but also shackled by per-country caps in the skilled immigration pathway and forced to wait 10-15 years before they can truly have the freedom to pursue entrepreneurship.
Rather than a total immigrant population (which includes temporary visas, student visas and even undocumented), a reasonable estimate would be to look at the principal workers in the employment green card category (almost half of employment green cards go to spouses & kids, especially for those from backlogged countries)
The numbers then make a lot more sense.
India moves into the top tier when you use a denominator closer to people who could actually found companies.
Adjusted for immigrant size and India falls from 1st to 18th among founders of US billion-dollar companies.
Indians are highly selected. About 82% hold university degrees, the highest rate, and receive roughly 71% of all H-1B visas. So they underperform their credentials.