Why exactly did Petra's grandfather want to see the film?

Ich bin neulich mit meinem Opa ins Kino gegangen. Er wollte den Film sehen, weil er eine alte Version gesehen hatte, als er jung war.

Answer - Because he saw an old version of it when he was younger

Translation: The other day I went to the cinema with my grandfather. He wanted to see the film, because he had previously seen an old version of the film, back when he was young.