Could it be true you can become bipolar from psychotic depression?

Not quite: A psychotic depression can occur in a patient who has bipolar disorder. People with bipolar i disorder can have marked ups (periods of elation or agitation, heightened energy & impulsivity) and marked downs (severe depression with or without pyschotic features). So the psychotic depression is part of the bipolar disorder. The depression did not 'cause' the bipolar disorder.

Vice-versa: I think you may have it backward. Bipolar mood disorder can cause psychotic depression. In some cases, psychotic depression may the first indication that someone has bipolar mood disorder. Psychotic depression does not "cause" bipolar disorder.