This reminds me of something I did to embarrass myself; I did like this years ago in a collaborative fan fiction game.
I wrote out a scene that included some mandarin words and phrases as part of the dialogue in an otherwise english-language scene. Ironically it was Battletech (I say that just because I've actually written way more in other games than BT) and the characters had Capellan origins/history.
I don't speak or write Mandarin, and rather than research.. oh I dunno "good" sources. Of all things I grabbed off my shelf the Firefly/Serenity RPG book off my bookshelf. Which included pages of some supposedly Mandarin words and phrases. I used that. (DUMB!!!!)
I wrote the scene, someone in the group did speak/read/write Mandarin and started politely but firmly telling me a lot of that stuff didn't make sense, was nonsense and/or gibberish.
I felt really embarrassed and rewrote the scene ditching the concept. I wouldn't do that again. I don't THINK anyone took it as racist, I certainly hope not, but it was bad. Even with good sources, I'd be VERY hesitant to attempt anything like that again. If I don't speak/write that language, I don't speak/write that language, period. That was a lesson learned for me.
I don't know if something like that, is what happened here. I don't know this author.
But I could understand if it was good in intention and just bad in execution. Because I've done it.
I'm very glad for that person in the group who said something and I appreciate the way they handled it and handled me frankly.
EDIT: I wanted to add, there's definitely a red line on this kind of thing somewhere for me, I'm just not sure where it is. Perhaps repeated behavior/incidents. Perhaps being called out and refusing to apologize or acknowledge the thing. Something in that ballpark.