I asked my choir teacher today how he learned to play piano (he plays decently after a year of hard-core practice) and he told me to start with learning the note for each key, which I already know, and then to practice caged arpeggios.
I googled it and all I can seem to find are guitar caged systems.
CAGED is a guitar system. It has nothing to do with piano.
Your teacher probably already knew how to play guitar and taught himself piano by learning to play on piano what he already knew on guitar. If you don’t play guitar, CAGED won’t be of any use to youl. Good luck.