The paper does not claim everything that you say it does -
"Wherever possible statistics on the magnitude of different forms of migration are provided, but these are drawn from available sources predominantly emanating from India which are largely based on educated guess and often politically biased as cross border migration is poorly researched in Bangladesh."
and
"It is argued that Bangladesh serves as a crucial reserve pool of cheap labour for the economies of Assam, West Bengal, Delhi, Mumbai and other parts of India. Thus Schendel (2005: 230) remarked: “If there were indeed 12 to 20 million unauthorized Bangladeshis in India, there were millions of Indians keen to employ them. The Indian state never developed schemes either to hold these Indian citizens accountable for their illegal practices of employing ‘aliens’, or to issue temporary work permits to labour migrants from Bangladesh."'
There are a dozen more caveats and provisos in the text that I could have referred to but I think this will suffice. Indians are very good at being selective in their quotations and references.