He could have said either 'ancient stars' or 'ancient generation of stars'. It's a stylistic choice. 'Some ancient generation of stars' created an image in the reader's mind of a group of stars existing at a certain point in time. By using the word 'generation' the author implies a direct connection between himself (a member of the present generation) and the ancient stars that created the very molecules he is made of. It is a way of saying that those stars are, in a way, his ancestors.
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