His FH is a very good stroke.
it looks a little WTA style because it is not as spinny and he has a quite vertical racket compared to the very closed/pronated takeback that most ATP players use but this only shows how meaningless those details are for getting power.
What mats is referring too is probably that JMDP doesn't use as much hips and legs like other players. that is just natural for tall athletes. just compare randy johnson to tim lincecum. people say if randy would wind up like tim he would throw 115.
however that just doesn't work. tall guys use the kinetic chain too but they do rely more on their levers than a super quick hip turn (like agassi for example). they just cannot turn that quick but that doesn't mean their legs and hips don't generate a lot of energy.
It is just that their "engine" works more like a truck engine with a large gear (long arms) while short guys like lincecums engine works more like a fast spinning race engine.