Ah, well, I in turn haven't watched the films.
It's a bit troublesome how confusing things get when the films doesn't quite convey the contents of the books - or in some cases when the films contradict the books - as most fans only keeps up with one of the media.
Now that I think of it though, I've seen clips from Snape's memory as it was portrayed in the film (hurrah for youtube) and if I disregard what I know from the books then I can certainly see how that clip could come across completely differently.
If memory serves me right, it excludes Snape using underage magic to hurt Petunia, Lily and Snape boarding the Hogwarts express for the first time and Lily telling Snape that she is fed up with attraction to Dark Arts after the episode in their fifth year.