It is possible to be born in Greece and still be India citizen. European countries like Greece do not give birthright citizenship. It depends on the situation and status of parents instead. If he is Indian, he cannot be Greek citizen as India do not allow dual citizenship. If he is Greek citizen, he cannot represent India.
Don't go with the wikipedia info. There Indian flag used besides his name because he eligible to represent India (as he yet not represent Greece national side) not because he hold Indian citizenship.
Note: Flags indicate national team as defined under FIFA eligibility rules. Players may hold more than one non-FIFA nationality.
Comments
If he is Indian, he cannot be Greek citizen as India do not allow dual citizenship.
If he is Greek citizen, he cannot represent India.
http://www.superleaguegreece.net/en/teams/team/platanias-fc-536/2017-2018-superleague-70/players/gkourzinter-singk-3057
Note: Flags indicate national team as defined under FIFA eligibility rules. Players may hold more than one non-FIFA nationality.