Does my dog have something wrong with it?

when I first got my dog (chilly) a pug the owner told us he was a hard one to train and yes its very very true but every time my dog sits down his doesn't hit the floor for some reason and when he walks hes legs kind of bring themselfs up way to high when he walks. He is a sweet dog and he was hard to train but this is weird. Was he born like that.