He was the antithesis of the modern player. Of course he trained, but his game evolved from his natural talent rather than a billion drills, physical conditioning and peds.
If I had to guess, I'd say he came up with that motion by trying to maximise slice and disguise rather than struggling to hit a ball, which I'm sure he just walked up and did.
Whatever he says, I'd take with a grain of salt. Like the old days, most of what he says seems to be more for effect than anything else.