Of the 358 occurrences of cuisine=beef_noodle, 253 were added in a single changeset across Taiwan. From what I can tell, they added this tag to every restaurant that contained “牛肉麵” in its name, among other bulk edits, some of which have since been undone. A similar changeset of theirs attracted some criticism about methodology.
@Graptemys added beef_noodle a couple years ago as part of a large-scale expansion of the table. I suspect they saw this usage, searched for “beef noodle” on Wikipedia, and came up with this description based on a quick reading of the Wikipedia article. The article is not well-written, but at least it makes clear that it’s talking about Chinese cuisine, even if the dish has spread to Southeast Asia via ethnic Chinese. I’m not sure any effort was made to examine actual usage of this tag in the database. The same edit introduced other definitions that contradicted OSM usage, even among Western cuisines. Still, it was a useful exercise in surfacing some cuisine tagging that had flown under the radar for a while.
牛肉麵 is the name for a family of Chinese beef noodle soups, as opposed to, say, fish ball noodle soups or stir-fry beef noodle dishes. The literal translation in English is “beef noodle soup”. Unfortunately, “beef noodle soup” also happens to be a common description of beef phở (as opposed to chicken or seafood) on restaurant menus in the West. This is only by coincidence, not because phở has anything to do with Chinese cuisine, but that’s why the Wikipedia article mentions phở.
Wikipedia has a dedicated article about phở that discusses the origins in more detail. The short story is that, as with a lot of home cooking and street food, no one really knows the origin of phở or even its name with certainty. Chinese, French, and Vietnamese people have all claimed it as their own invention, but the reality is more complicated than that. The dish itself has evolved over time, so that whatever it came from is no longer recognizable as the same dish. (Neither pot-au-feu nor stir-fried water-buffalo phở sounds particularly appetizing to me.)
The cuisine=noodle tag lumps all noodle dishes from all Asian cultures into the same category. Sometimes this stereotype is convenient; other times, it’s terribly inconvenient. What Westerners colloquially call “noodles” could be mein (麵) or fun (粉) or other things that Chinese people normally distinguish as quite unrelated concepts. Vietnamese people make even more fine-grained basic distinctions: mein could be mì, bún, etc. Some restaurants serve a wide variety of noodle dishes, while others specialize.
If I encounter a cuisine=noodle in a random town in the middle of the U.S., I assume it’s a noodle-themed restaurant like Noodles & Company (serving anything in the shape of a noodle, from pasta to chowmein to ramen). Or cuisine=vietnamese;noodle would be a “Vietnamese noodle restaurant” named “Phở [insert year]” that devotes the first two pages of the menu to phở and the latter four pages to other noodle soups, noodle dishes, beef stew, claypot fish, and assorted rice dishes that might be better than the phở.
On the other hand, in an ethnic enclave, some restaurants will specialize further. For example, in a Little Saigon, a restaurant will advertise itself as a bún, bánh canh, or phở restaurant. You can probably order bún from a bánh canh restaurant, but you’ll probably regret it. I’d like to use these dishes as cuisine=* values, but usually I just go with cuisine=vietnamese. I avoid cuisine=noodle in these cases, to avoid leaving a false impression about their flexibility.
In Vietnam, the tagging scheme breaks down even more. Typically, each stand only serves one noodle dish. cuisine=vietnamese is stating the obvious, and cuisine=noodle is rather meaningless given all the options.
We would be better off splitting the cuisine=* tagging scheme into dishes versus traditions. In the meantime, I suggest correcting the documentation to clarify that it’s only about the Chinese dish. That’s how it’s being used in the database, apart from one restaurant in Singapore that used to be tagged cuisine=Beef_Kway_Teow,_Mee_Pok before being retagged by a self-described “experimental data analytics bot”.