Grain - Or lack thereof

I'm talking about this picture:I took this a couple of months ago. I shot it on Ilford HP5+ and then scanned it in at 3600 DPI.I then printed this picture around 15 inches tall.HP5+ is an ISO 400 film. It's supposed to be grainy. Well, "supposed" due to physics.You can definitely tell the grain in the sky. But when I look at the details on the roof the conservatory, I see nothing but pure detail -- no grain and no pixels.The amazing thing is that this is all old tech.And the old tech is sometimes as good as the new tech.