I think it's frutiger metro : Mostly, it combines flat, minimalist graphics with a maximalist design philosophy, typically catering to a pre-teen/teenage demographic. Frutiger Metro shares a lot of similarities with Frutiger Aero and other aesthetics of the time; unlike Frutiger Aero which has a large focus on detailed glossy 3D designs, Frutiger Metro is flat.
In the mid 2000s, this tween / teen aesthetic was all over the place, alluding to contemporary urban dynamism, with Punky collage and HipHop influence. It was even the default aesthetic of school supply.
It may share some similarities with Hipness Purgatory : a renewed appeal for crafty materials and handmade doodles (in opposition to corporate digital aesthetics). The video game SSX one tour (previously very Y2K) perfectly synthesize both aesthetic.
