He looks like a half

Correcting student papers today, and I got this sentence (students are writing about their favorite musician):

"He looks like a half, but he is a pure Japanese."

I know fighting against this use of "half" here is an uphill battle, and my own "half" kids who've grown up part here and part abroad aren't bothered by it, but I was wondering how the rest of you approach it with your students?

(In this case, I corrected it to "He looks mixed race, but he is Japanese.", but that didn't totally satisfy me, since one can be both mixed race and Japanese.)

EDIT: Thanks for your input. I get that the student wasn't being offensive. But I don't think describing someone as "a half" or as "pure" whatever race would come across well if the student found themselves communicating with English speakers who aren't familiar with Japanese English.

I think I like the suggestion "He looks like he is half Japanese, but he is full Japanese." as it's in line with the student's English level.