Also: don't be dissin my boys Wheatus. What, you want the poor kid should just hang himself in the third act or something?

Given the fact that the high-pitched Brendan sings both his and Noelle's parts, I've always just been under the impression it's a fantasy/dream sequence thing. Like in Fast Times but without the walk-in. This opinion is reinforced by the soft filter applied to Tara Reid (if I recall correctly) in the video, traditionally signifying dream sequence.