Manga Genres

A new book came into our store recently: Manga for Dummies by Kensuke Okabayashi. It turned out to be mostly a how to draw book, but in the first chapter it discusses genres. I know there's a lot of misinformation/mistranslation to be found on the web and in magazine articles, but some of the following don't match what I've been reading about (and there's no mention of josei manga).

The list from the book:
Kodomo Manga: Comics for little kids
Shōnen Manga: Comics for teenage boys
Shōjo Manga: Comics for teenage girls
Seinen Manga: Comics for young adult males
Redisu Manga: Comics for young adult females
Shōjo-ai Manga: Romantic comics for teenage girls
Shōjo-ai Yuri Manga: Romantic comics for lesbians
Shōnen-ai Manga: Romantic comics for men
Shōnen-yaoi Manga: Romantic comics for homosexual men
Seijin Manga: Comics for adult males
Redikomi Manga: Comics written by women for late teen to adult women, depicting more realistic, everyday accounts; literal translation: lady's comics
Seijin Manga: Comics for adult males
Dōjinshi Manga: Comics written and illustrated by amateurs (usually circulated among a close group of other manga amateurs)
Yonkoma Manga: Four-panel comics, usually published in newspapers
Gekiga Manga: Comics focusing on serious topics; geared toward mature audiences
Ecchi Manga: Comics focusing on heterosexual/lesbian erotic themes (softcore pornography) read by men
Hentai Manga: Comics focusing on hardcore pornography

So, did the author misinterpret or make up some of these definitions or did he have better source material for current definitions in Japan?

Most of those seem...off to say the least. Kodomo, shonen, shojo, and seinen aren't really genres at all; they're demographic markers (I'm guessing that "redisu" is somehow an equivalent to josei). Doujinshi and yonkoma don't necessarily qualify as genres either since those terms are more descriptive of the production process and/or format than the actual content.

I suppose it's possible that the author of the book has better source material for definitions, but it seems much more likely that he's misinterpreting them (or just making them up).

I'd take this information with a healthy-sized grain of salt, myself.

I'd lean towards misinterpretation over better info - a lot of these seem really off as shadrach_anki described.

Shōjo-ai Manga: Romantic comics for teenage girls
Shōjo-ai Yuri Manga: Romantic comics for lesbians
Shōnen-ai Manga: Romantic comics for men
Shōnen-yaoi Manga: Romantic comics for homosexual men

That is just all off. Shoujo-ai, shounen-ai, yuri, yaoi - it's all about homosexual relationsihps, not about who the manga is targeted at. Shounen-ai and yaoi readers seem to be primarily female - these books are definitely not aimed primarily at a male audience, and I believe a large proportion of authors are female too.

An important aspect of doujinshi is that it often uses established characters and settings for new stories done by someone other than the original author, or outside the usual scope of the story line. You get professional manga artists doing doujinshi based on other people's series, you even sometimes get authors doing doujinshi of their own series.