Even in that picture, he has male-specific red coloration over the bows of the wings - this is not always present, but when it is, it always indicates male, as long as it's not part of the coloration of the rest of the bird. I think it was pretty obvious it was a roo, but it may not have been to whoever sold you the bird, if they haven't had a lot of experience with birds of his coloration and identifying males from seeing the male-specific red over the wing bows.
He's an absolutely gorgeous bird!!! You should have no trouble rehoming him, if that's what you need to do.
