I don't really see your point, at all. Aladdin is a magician and if magicians across all stories and lore share one thing (aside from magic), it's that they are secretive folks and not blabbermouths. Besides, there's not really anybody to tell about it. He wants to go to Magnostadt by himself and thus giving Alibaba and Morgiana more things to worry about would do no good. Like he told Hakuryuu earlier, he doesn't want to choose sides and wage wars for anybody's sake, though he would defend his friends, so telling the local authories to make them hate Magnostadt even more wouldn't be his style.
I'm only happy we, the audience, learned it (although I suspected as much even before), because it makes Magnostadt look all the cooler.