Yes oranges are all right for dogs. Within reason of course! Too much too often would be too acidic, especially against his teeth. But as an occasional little treat it's fine.
Dogs like a bit of apple too! Again not too much, maybe a quarter apple for a small ish dog. But make sure he doesn't eat the seeds, as they are toxic.
Oranges are great!!!! Bet he enjoyed them...No, it won't hurt him!!! :)