This clip is mainly used online as a cute-meets-gross reaction sound rather than for a widely documented film, game or TV reference. The uwu phrasing comes from internet and anime-adjacent meme culture, where soft, babyish text and voices are used for irony or parody. Sounds like this spread through short edits, voice memes and chat posts because the contrast is immediate and easy to understand. It stays popular because one tiny burp can instantly turn a wholesome setup into an awkward joke.