I also met him twice, but was too ignorant to know about this mystery at that time. Another mystery is: who is Reiko Nomura? There is a piano teacher with the same name on this site:
http://www.puretone.jp/school.html
I sent an email in Japanese by using their inquiry form, but haven't received a reply. I asked if she is the same Reiko Nomura who played piano on this album. I also explained that we have this mystery of not knowing who arranged the pieces.