Beauty and the Beast doesn't play a lot of games with its narrative technique. Third-person omniscient allows it to move around at will, showing us whatever we need to see and letting the story unfold in a rational, linear fashion so that it doesn't lose us. This is a family film, after all, and the more straightforward you can keep the narrative, the easier you'll hold the attention of the little guys.
The big exception—and it's not all that big in the grand scheme of things—comes in the opening. A voice-over narrator (David Ogden Stiers, who's also the voice of Cogsworth) quickly gets us up to speed on how the Beast got to be the way he is and clues us in to the stakes involved in the story we're about to see. The narrator never returns, and except for the stained-glass window shot at the end, there's no real shout-out to it in any other part of the film. It's simply an expedient way to tell us what we need to know before the story properly starts.
That's not normally something you do, delivering a whole lot of story information in such a big, ungainly mess. Writers call it "telling, not showing." If you're telling a good story, you want to stay away from just shoving information at the audience and instead let it unfold naturally and subtly. In most cases, when you see something like that in a movie, the writer has either given up or just doesn't have time to tell us that part of the story properly.
The backstory in Beauty and the Beast, however, might get in the way of the main story, which involves how Belle came to be at the castle and what she did to break the curse. It would slow things down since we're basically all waiting for the romance to start. Showing us the Beast as a snotty little kid who gets cursed would just delay what we all came here to see.
So, we get the short version, delivered gently but expediently and then set aside in favor of a "show, don't tell" format that writers tend to approve of. The idea of using stained-glass windows to convey the bullet points is a smart one. It gives the story a little visual flourish while staying distinctive from the rest of the film. That's how you turn a potential narrative shortcoming into an asset and what separates a merely good film from a genuine classic like this one.