night of a million stars. But shouldn't a million stars be
百万星? Moreover google translates
six stars. Is this a translation error? If not, can anyone explain why?
六等星【ろくとうせい】 is definitely "a star of the sixth magnitude" or "6th magnitude star", not "six stars" nor "million stars." So it's an error made by Google Translate.
Google Translate recently started to use a neural network. It works excellently for many common sentences, but I feel it also makes terrible mistakes like this one when it encounters relatively rare words. From my experience, it's especially bad at dates and numbers.
By the way, 百万星 doesn't sound natural to me, either. You usually have to use の and say 百万個の星, 百万の星々, etc.
EDIT: I've found that there is one (and only one) fantranslation of the song that actually uses Million Stars. I believe it's a human error, but there is a small chance that Google automatically "learned" it as a translation of the title of this song.