things could go either way from this point, the mangaka could make it so
that the only people who heard him call the black magician Rood are the
ones close as in Hadelio (who already knows), the purple haired guy
(who's 99% positive it's Rood and is a huge fanboy anyways so it wouldn't hurt for him to know), Lid's brother (who I'm guessing will no longer be an antagonist after this incident)... so the secret won't be completely out. But the mangaka could also make it the way you see it, as in everybody heard Lid call him Rood and the secret is out. But even that won't be a big incident since the tower, the association and everyone that matters already knows so adding some students to the equation won't change much