They use the skeleton, not the model. I mean, grab a naked male night elf and a zandalari troll and you'd have to be willfully blind to miss the obvious differences, especially the horrendous animations male night elves have on top of their low rez hair and skin options not to mention the atrocious customization options (females get markings but males only get hobo beards, even though malfurion has face markings).
The casting animations are not even the same as male night elves. Which is a good thing.