Well, there was foreshadowing to Cinder's arm in Volume 4Salem mentioned her 'treatment' and how at one point Cinder was gasping and groaning in pain while her arm twitched. She also gripped her arm after Ruby used her silver eyes to save Jaune in Volume 5. And the Lancers aren't odd, compared to the rest of the Grimm. Ozpin being cursed by the gods is also not that strange considering we now know that magic does indeed exist in RWBY