At BlizzCon 2010, it was mentioned in an offhand comment something called a "dragonman" was based on unused concept art for a scrapped idea for a playable race. These are likely that "dragonman" as that is their model's name.
Dragonmen use the same model base as alliance worgen and therefore use the same animations.
This article or section includes speculation, observations or opinions possibly supported by lore or by Blizzard officials. It should not be taken as representing official lore.
These creatures are likely the Scourge's mad scientists version for the Black dragonflight. It's likely they were first created as an experiment by Nefarian to have the capacity to create other experiments for him. The Aberrations that appear during the fight with Maloriak support the idea that the dragonmen were created, but unknown from what. It's possible humans were experimented on with dragon DNA.