There's a partial precedent for this: a couple of years ago a husband-and-wife team released an animated film called
The Summer of Mermaid (which one of the filmmakers
uploaded to YouTube just over a month ago in an uncanny display of foresight) that also went viral but didn't break out to nearly the same degree. That's partly because it just didn't have the same outsider-art patina—for one thing it had actual marketing, plus a baseline of technical competence that's completely missing in
Niu Lai, which somehow looks worse than those '90s direct-to-video Pixar knockoffs with titles like "An Insect's Life" or whatever.
Summer of Mermaid also wore its influences on its sleeve and came off as a bad Miyazaki pastiche, whereas
Niu Lai is rather less easy to pigeonhole that way.
But I think the most interesting difference is that
Summer of Mermaid had support from local cultural/tourism bodies and looked enough like a "real movie" to get advance puff pieces positioning it as a milestone in Chinese independent animation, building up some awfully unreasonable expectations and all but inviting a backlash.
Niu Lai came out of nowhere and is something the online grassroots can plausibly embrace as their own, since without them the movie would've disappeared into total obscurity after making less than $2,000. And when
Summer of Mermaid got picked up by international media, it was an example of vicious Chinese netizens dogpiling a scrappy independent labor of love, which inevitably filtered back to China and made the discourse around the movie (which wasn't really as vicious as all that) much less entertaining. The coverage of
Niu Lai is framing the haters as stick-in-the-mud authority types (cf. "state-run outlet Beijing News") putting up "NO FUN ALLOWED" signs, which reinforces the grassroots discourse—one reason people are rushing out to theaters to see it is because there's a conviction that the regulators will pull the film at any moment, which I doubt will happen (all movies in China go out with a preset KDM expiration date and I think it's more likely they'll just reject any request to extend it) but illustrates how this is bound up with a bit more than ironic shitposting for its own sake.