ZoRo DiDn'T uSe HaKi In AlAbAsTa-
The concept for BOAT is repeated word for word by Hyo when talking about Ryuo aka haki
and the guy telling Zoro about that is taught in the Wano way, it's all in the panels below
The same guy that explains BOAT, aka haki, is the same guy that teaches Zoro snatch, aka sunacchi, i.e. a battle cry in Wano. The same guy also has Wado Ichimonji, the blade forged by a guy that left Wano 50 years ago, whilst the guy possessing it is 51 years old. Him having Wado, knowledge of BOAT/Ryuo/Haki, snatch, irrefutably points to him being taught the Wano teachings.
Now the SBS confirmed that he is from Wano and taught in that way.
Haki is called Ryuo in Wano.
WhY dIdN't ZoRo UsE iT
Zoro didn't master it yet and couldn't bring it forth voluntarily.
Therefore