Psychosis during/as mania isn't uncommon. In the Diagnostic and Statistical Manual of Mental Disorders (DSM), used to diagnose people in many cases (sometimes the ICD is used instead, which uses "affective" in the name, so maybe they've used the ICD), BP (bipolar disorder) is "technically" not a psychotic disorder. Mania is sometimes still considered a form of psychosis.

However, in the past, mania and were seen as forms of psychosis and (so) BP(-I) was seen as a psychotic disorder.

I think it should be called a psychotic disorder and mania and depression should both be seen as forms of psychosis. Now, people often only think of hallucinations and specifically hearing voices as psychosis. Many people can have mild/"background" hallucinations, though, without having BP or SZ (schizophrenia).

Being severely depressed, it could be that understimulation is the cause of hallucinations. Are hallucinations your main problem or also delusions, beliefs that are very strong, purely (started as) assumptions/epiphanies and make normal functioning difficult or impossible (they don't have to be wrong)?

Do you experience, or have you experienced, any euphoria/elation/ecstasy or lots of activity during the period of depression? If that isn't the case, a mixed episode is maybe not very likely.