Siddhartha belonged to the Shakya's Kshatriya clan and tarai region of Nepal.The region is still populated by Indian origin (Madhesi People).I did read this, and it seems strange.
The author mentions that most major civilizations formed along the banks of a great river... Yangtze for China (wrong... it was actually the Yellow River in Northern China)... and the Indus River for India. Giving India claim as a civilization state.
Which would make sense if we were talking about British India. But not the Republic of India, since the vast majority of the Indus River exists in modern day Pakistan.
And from what the Pakistani members have been saying, they fully oppose Indian claims over this river or any history related to it.
So when the author talks about "India" they seem to be talking about the entire South Asia, which the Pakistani and Bangladeshi members here strongly oppose.
It's like when we mention that the Buddha was from Nepal, the Indian members here say "it's the same thing as India". But it's not? India is not the same thing as South Asia, just like China is not the same thing as East Asia.
Other important sites of Shakya Confederacy like Gorakhpur belt,Pava,Shravasti,Kushinagar etc (Buddha circuit) is in modern day India not Nepal.
In any case it was India which made Siddhartha as Gautam Buddha when he attain "enlightenment" at Gaya again in modern day India.All his former Gurus like Alar Kalam,Mogiliputttissa etc belonged to India.
China itself is made of several non Han ethnicity.