I'm really into retro computing having collected over a hundred 80s 'home' computers (all non-PC/Mac), including at least a dozen Japanese models, but have never heard the term "PC-98" to describe a particular style of pixel art, probably because I don't speak Japanese and haven't lived there. However, I do see some traits in how the examples shown were constructed which strike me as unique beyond just the obvious Japanese aesthetic of the content.
While the article highlights that Japanese computers had greater memory and graphics capabilities earlier due to the need to represent more complex fonts, there's another factor I suspect is behind the differences I'm seeing in those images. Japanese business computers tended to have analog RGB output and displays earlier and more commonly than those in the U.S. Of course, analog RGB was available in the U.S. around the same time but it wasn't usually considered worth the increased cost for mainstream desktop use in the early 80s. Monochrome or 4 colors were generally considered sufficient for 80-column capable text displays (~640 pixels wide).
Some of the dot patterns I'm seeing in those examples work well on RGB displays but wouldn't work as well on composite video displays or TVs. In the US, early home computer pixel art targeted resolutions like 256 x 192 and 320 x 200 in 4 or 16 colors but generally assumed the pixels would be displayed on a TV or composite monitor and so leveraged the pixel blending and additional artifact colors composite video can uniquely create to enhance their artwork. These composite-exploiting blends and colors are lost when those images are displayed in RGB, leaving only the original pixel patterns which aren't what the original pixel artist saw or intended when they created the image (which is why original composite-targeted pixel art is best viewed on a composite CRT or CRT emulation). I think these Japanese artists being able to target analog RGB output is behind some of the subtle (but cool) uniqueness I'm seeing in the "PC-98" pixel patterns.