A Conversation with God Himself?

This isn't really my experience, this is my grandpa's famous story he's told me time and time again. It happened back when he was about my age.

My grandpa's mother, my great grandma had to undergo brain surgery to remove a tumor, the surgery was successful but unfortunately it was cancerous.
The Doctor that preformed the surgery told my grandpa and the rest of the family there was nothing they could do for her and the doctor gave her 1 year to live.

About a month later my grandpa was walking to a friends house when he noticed a man that was dressed in pretty trashy looking clothes, who came out of a nearby house. He walked by and said "Hi". My grandpa turned around and said "Hi" back.
"Nice day isn't it son?", asked the man. "It's ok, I guess", said my grandpa.
The man then said to my Grandpa "I heard what happened to your Mother Son, I am truely sorry, but you have to understand, its not over yet man, you have to keep your faith, OK?"
My Grandpa looked at him like how did you know. The man then offered a handshake to Grandpa. Grandpa accepted then the man said "She's going to be OK Mike, I give you my word."

They walked off and the man turned left down the street and eventually was gone out of my Grandpa's sight.

Grandpa never saw the man again but my great grandma lived over 20 more years. To this day my grandpa, God rest his soul, believes he was talking to none other then God himself.