The method which supposed to return YES or NO obviously should return boolean, not String.

"YES" and "NO" are strings, not booleans, and all other languages have the same output, so, no, it won't be changed now. All solutions would be rendered invalid if changed.

The name of the function, it could be changed, but with care, again, so not all previous solutions become invalid.

I think your issue (maybe suggestion would be better in this case), while it has some valid points, should have been raised before the kata was published, now it seems too late.