Hard to say yes or no as to whether there was psychosis. Did the doctor send you to a neurologist? My understanding is that, brain scans are performed to rule out injuries, lesions or epilepsy before categorizing under a mental illness.
Having mistrust of others, alone, I don't believe is psychosis, per se, since there could be external stimuli leading up to such beliefs. Mistrust as in feeling others are discussing you, behind your back. If your grandma, declared psychosis, is there a family history or a tendency to overshare information within a social setting?
What did the psychiatrist say?

Sent from my LGMS323 using Tapatalk