In Japanese there is no distinction between kanji and hanzi, they are the same thing, and written equally - 漢字.

In English, it would be most appropriate to call Chinese language characters hanzi, and Japanese language characters kanji, but this is an English distinction, not one in the native tongues that use these characters.

As the author of these drawings is Japanese, the correct term would be “kanji”, but the word “kanji” literally means “Chinese character”.

Not intentionally I don't think, but people might do that if they're not sure which language the characters came from or if they just don't know the term "hanzi".