Is the only source for this the play-asia listing? It's weird, I haven't been able to find anything about it anywhere else.
Also, we have a few official credits early thanks to a
Yamaha piano sheet listing (italic names are google translations for which I can't be sure of what themes they correspond to):
1.
Opening theme - Yasuaki Iwata (Title theme ?)
2.
Information office - Yumi Takahashi (Resident Services ?)
3. Island Tour at noon (sunny) - Yumi Takahashi
4. 9:00 a.m. (sunny) - Kazumi Totaka
5. Nook's Cranny (upgraded) - Yumi Takahashi
6. K.K. Birthday - Kazumi Totaka
7. K.K. Disco - Kazumi Totaka
Small note: if track 2 is indeed the Resident services theme, then it should credit at least another composer (since it's a medley of Town Hall from ACNL and Nook's theme from the original AC). So these might be more like "music by" credits than "composed by".