We don't know enough about that to say that he actively pursued Hermione. Remember when Harry and Luna somehow found themselves under mistletoe too, in the previous book? Luna quickly escaped as well.

For all we know, McLaggen was going on and on about Quidditch and ended up walking under mistletoe. Hermione, being as annoyed as she was that night, would obviously escape.

McLaggen's caricature of a character wasn't written to be much more than a braggart and annoyance. The film added in the creep factor and several 'flirty' moments or whatever they were.

I suppose we could argue that McLaggen barely, if at all, pursued Hermione in the book.