Yes, this is GBA music! To clarify a little, GBA doesn't have any supplementary audio hardware besides the four Game Boy channels. This means games generate music in software. Nintendo supplied a sound driver which by my count about 70% of games used. What you see here is a representation of the sound driver's internal tracks alongside the Game Boy channels. (The three channels to the right are Game Boy channels.) The audio is mixed with a much higher quality than the GBA driver performs. This was made possible with the awesome music player, agbplay by ipatix, who implemented individual channel export for me:
Visualization (oscilloscope view) was done with Sidwiz 2 by CapteinKuK and RushJet1. Music was composed by Atsuhiro Motoyama.