We can't be sure.
This appears to be one of those loose ends that was never really cleared up. We're not really given any description in the books - they're essentially just described as 'surly'. And they're not ever described - or mentioned again - in the books ever again. So... we can't know.
While searching through Pottermore, though, for some information regarding dwarfs, I found this interesting bit about Red Caps:
These dwarf–like creatures live in holes on old battlegrounds or wherever human blood has been spilled. Although easily repelled by charms and hexes, they are very dangerous to solitary Muggles, whom they will attempt to bludgeon to death on dark nights. Red Caps are most prevalent in northern Europe.
Fantastic Beasts & Where to Find Them, courtesy of Pottermore (emphasis added)
The Red Caps are described as being 'dwarf-like'. Now, this may be just a coincidence, and it just means short, but it could also be interpreted as being that they're similar to the dwarf species.
Interestingly, the Red Cap looks very similar to a house-elf:
(and also bear a resemblance to Goblins)
So there's a slight possibility that all those small, humanoid, pointy-eared species are related, and that dwarfs are actually a part of that family, given that they all look so similar, and that the Red Caps are described as being dwarf-like.