Is "this theme" the theme of a position with unique proof games of different lengths?
No, it's a different theme. I wouldn't have said "shortest" for a thing like that.
My suggestion would be to identify the comment(s) in which "this theme" occurs.
Please don't use computers. I did a test already. It's sound.
Hardly original, but seems to be the shortest possible problem of this theme.
Is "this theme" the theme of a position with unique proof games of different lengths?
No, it's a different theme. I wouldn't have said "shortest" for a thing like that.