Schizophrenia used to be distinguised from BP (only) based on prognosis, whether it would get worse or better over time. Now people have realised that schizophrenia can have a very good prognosis. At any rate, after a psychosis things will always improve. Maybe it won't ever happen again (that's not at all unlikely).

All it means is that there's a propensity or risk. That risk has always been there. That doesn't mean something like this will ever happen again, especially when it was drug-induced.

Just one (drug-induced; likely so-called "brief") psychotic episode doesn't warrant the schizophrenia diagnosis (that's not just me: according to the DSM).