It's following on from the term "blackfishing" which is where non-black people deliberately adopt not only black mannerisms and hair styles, but cake on dark foundation in order to make themselves appear ambiguously black. See for example: the entire Kardashian family. There is also "brownfishing" which is a slightly more general term which refers to the same practice but as applied to a lot of ethnicities. For example, Ariana Grande's ambiguously Latina look, while being resolutely white (compare her now to what she looked like back in Nickolodeon days). "Asian fishing" is then the logical extension of these. Alternate terms that might apply are blackface, brownface, and yellowface, although these tend to be more explicitly negative caricatures to mock different ethnicities.
While I take your point that "Asian" is a somewhat nebulous term and there are lots of different Asian ethnicities and cultures, for better or worse westerners tend to associate the term "Asian" primarily with East Asia. But that doesn't change the fact western (white) people are deliberately trying to co-opt East Asian aesthetics for social (and sometimes, actual) capital which is definitely an issue that needs to be considered. Splitting hairs about terminology is somewhat counter productive in this regard as in the meantime sooner or later they may well try and do the same thing with e.g. South Asian ethnic features or cultural traditions.
Your objection is basically a circular "whataboutism" which deflects from the actual issue by claiming those pointing out this fundamentally appropriative if not outright racist trend are themselves racist, in the process giving a free pass to the actual people doing it!