He knew a lot about his grandparents - and perhaps he feels he's been endowed with abilities to go into people's heads who are long dead - but, to a certain extent, he's making it up.
“And that's one thing that helps me is I learn it blandly, vanilla, then I don't try to act it too soon because you start to act it, and you kind of go away from what the next sentence is, what the next paragraph is. So get it down so it kind of can - it's in there so you can then, as I call it, danc”