If we're going to treat this Cho Chang theory as worthy of serious consideration:
As a PP noted, Cho is also a Japanese forename (female), albeit of relatively recent vintage. My landlady in Phnom Penh was also called Cho (and I know she spelled it that way as she left me notes in English). But the character Cho Chang is British; there's no suggestion she was born abroad. We don't know when/from where her ancestors came to alt/UK. Perhaps the parents came from different ethnic/national backgrounds and met in the UK.
I've lived in China and Japan (and Cambodia) where, as in Europe, there's a long history of intracontinental migration, commerce, and cultural exchange. You come across all kinds of oddities among person names, place names, slang, etc. even in the historical records - even in Japan, which was the exception-that-proves-the-rule with its long intentional isolation. There are "Chinatowns" all over east Asia (and beyond), and Chinese elements are incorporated into local language in diverse forms. Names traditionally associated with one country are adopted, mixed up, blended. Languages evolve, people travel and read, elements get borrowed.
Last names become first names and vice versa, either accidentally or on purpose. They get flipped by immigration when someone moves to a country which uses a different ordering convention. There may be multiple methods of standard transliteration for the same source language/alphabet. Parents in a diaspora country may tweak a name to work in the new language, or may even make a mistake in the spelling/pronunciation if they're not fluent in the original language. It's also possible that "Cho" is a diminutive or nickname.
If Rowling had said something arguably racist, either in the books or on record elsewhere, about the reason behind the name or how she chose it - then sure, critique that.
But since we're entertaining assumptions without evidence today, let's look at the likely assumptions underpinning this "Cho Chang's name = JKR is racist!!" theory. Potter is littered with names of mixed European origin: Minerva McGonagall, Blaise Zambini, Bellatrix LeStrange, Florean Fortescue. But spot an Asian name that appears to borrow from multiple cultures/vary from traditional patterns annnnnnnnnnnd ... burn the (witch) racist!
Could this be racism on the part of the authors of these theories and the people who repeat them uncritically, rather than on the part of JKR? Why assume that Asian cultures are static, separate, and isolated when we know European countries have swapped and borrowed language all over the continent? Why freak that someone with Asian ancestry might have a forename that was traditionally used as a surname when we're happy to accept Huxley, Austin, Rafferty, Kendall, etc. as first names for white British/American babies? Why assume that nothing other than a "traditional" name from the family's (presumed-unitary and inflexible) culture of origin is allowed for someone of Asian heritage, when we all know of white babies called Brixlynn, Indy-Rose, and Khaleesi? Why this required purity for "Asians", specifically? Especially when we apparently don't even know which Asian countries/cultures are relevant?
Anyway, whether or not this Cho Chang conspiracy theory itself should be branded "actually racist" and its creators summarily canceled complete with angry tweets from children (and MPs), it does point to a very young, probably very sheltered person who believes that he knows everything about "how things work" because he uses the internet a lot, but has very little first-hand experience of the breadth and variety and sheer glorious messiness of real life diversity. And little knowledge of any history beyond (perhaps) his own.
Incidentally, there's a character called Chang Chong-Chen in Hergé's Tintin series, which sounds pretty damning based on this very convincing Twit Logic. ( OMG, was Hergé a racist??? 
Am I going to have to burn Red Rackham's Treasure? 
) Wait, maybe not: the name is a nod to Hergé's friend, the Chinese sculptor Zhang Chongren, and the two came up with the alter-ego's name together.
TLDR: It's always best to consider ideas in context, kids, before you go off half-squawked. And do your research from primary sources.