Coincidentally, a colleague has just provided more information:
I said "Under the tax treaty, the individual will only pay tax once (the purpose of the treaty is to prevent double taxation), and will pay tax in the country of domicile. See this:"
"Vaibhav Sankla, Director H&R Block India explains, "If a US resident earns Government pension from India, his pension is taxable ONLY in US if he is a resident of and national (citizen) of US. So if a US resident is not a citizen of the US, then irrespective of whether he is a green card holder or not, his pension income from the Indian governmentwill be taxable ONLY in India."
Since Patel is not a US citizen but just a green card holder, he will have to pay tax on that pension ONLY in India.
Article 20 states:
Any pension, other than a pension referred to in Article 19 (Remuneration and Pensions in Respect of Government Service), or any annuity derived by a resident of a Contracting State (in Patel's case, US) from sources within the other Contracting State (India) may be taxed only in the first-mentioned Contracting State (US).
According to the above, if a resident, green card holder or citizen of US received private pension or annuity from India, then that is taxable only in US"
Apparently the tax treaty makes a noncitizen of US taxable only by India on nongovernmental pension from India sources.