Wow 8.5, that is a big one.
I actually lived on Sumatra for about a year. Little place called Prabamulih on the road to Palambang near Batu Raja.
I rented a house that was pretty much in the middle of no where but pretty nice by Indonesian standards.
One day my car broke down about 200 km away from home and I thought I was screwed (no AAA auto service there). Five minutes later a car stopped to help. I ended up getting a tow back to Prabamulih by the guy. After the driver and passanger got out to see what was the matter, I heard his passenger tell the driver who I was, who I worked for, where I was from and where I lived (all in Indonesian) even though I had never met either before.
Nice people over there in central and south Sumatra. The ones in the north are not so.