Not quite, the diplomats are given exemption from tax that are included with the ticket price. But they are only exempted if the ticket is for themselves or family.
Do US government need to file taxes in India? This is the US government bought the tickets for the refugee that seek to immigrate to the US and the refugee will later pay back those airfare payment. In a way US lent the money to the nanny family to buy the airfare and pay back the US government in later time.