The difference applies to "Some of the data prior to 1902", not all of it. It is a footnote that goes with the asterisk for the 1901 listing of 295,215,000 but a second look reveals a second, additional, listing for 1901 of 270,183,000.

Regardless, what the chart does reveal is that the population appears to be relatively stable until after WW-II. The population growth trajectory goes skyward after that. It's no wonder India passed the Wildlife Protection Act of 1972. By then the population was more than double what it was in the days Corbett shot the Champawat Tiger and the Panar Leopard.

To put it into more perspective consider India has added a billion people over the past century. Those billion people have to live somewhere, eat something, create SOME waste, and travel on roads that go nearly everywhere.