-u 3 gives you Katakana. To include complex Kanji (Chinese characters used in Japanese), you need a custom character set. CMatrix doesn't do this natively, but you can pipe virtual input.
The characters weren't random. Leo noticed it immediately. cmatrix normally spat out a random stream of ASCII. But this... this was forming fragments of words. cmatrix japanese font
jp2a --width=80 --height=24 some_cyberpunk_image.jpg | cmatrix -u 4 -s -u 3 gives you Katakana