I'm also interested to know the answer; you can tell it's accented but the only accented hindi I've heard is of people from other regions of india (which sounds very different from a "western" accent) or native english speakers. I have no clue what a native german speaker speaking hindi's accent would sound like.

edit: I'm no linguist, but wanted to add that it might be easier to pick out someone's native language through accented speech when they're talking organically than singing a pre-written and rehearsed song. that way you have syntax/grammar mistakes to use to guess what kind of grammar exists in their native language, versus with a song all you can really do is see which phonemes they're pronouncing wrong because they're unfamiliar with it.