If you are a non-resident of the United States, you are not subject to any Federal tax (Income tax) at the time of exercise or at the time of sale (capital gain). Amount that you see which is deducted is a mechanism of ‘sell to cover transactions’. This involves the employer selling a part of the allotted stocks to pay for your Indian Income tax. Such deducted amount would have been transferred to your employer who will use the same to pay the TDS.Since there is no double taxable, question of DTAA relief does not arise