Dual citizenship is given to citizens of those countries which allow dual citizenship. Since Pakistan and Bangladesh both allow this, this becomes a possibility.
But then Para 7 of the Citizenship Amendment Act 2003 has the following line
(ii), but does not include a person who is or had been at any time a citizen of Pakistan, Bangladesh or such other country as the Central Government may, by notification in the Official Gazette, specify.
I guess that rules out citizenship for all the people Advani is concerned about.