what style is this?

[charlie foot]

In Hsing-I the basic horizontal punch is beng one of the 5 fundamental fist techniques- typically drilled in an advancing footwork step.

Bawang said it first Northern Longfist has this also- a horizontal punch hitting in succession- cha- to hit in succesion.

by a boxer's speedbag work i assume u mean the quick succession of over-hand punches

yes exactly this.. like a horse hitting with its hooves.