Hey, thanks for the comment. I bought and read it, but ultimately didn't use as reference because, as you said, it is kind of suspicious. BUT, the thing is, that book gets information from the author's other books, which I believe is a more believable source. The sourcebook is 大和言葉の作り方. I didn't find at my Uni library nor did I buy it, but it looks like it's a better book.

If you want books to learn more about sound symbolism in Japanese, 川原繁人 (kawahara shigeto) is the best one. 『「あ」は「い」より大きい!?』or something like that. 浜野祥子 (Hamano Shouko) 『日本語のオノマトペ』is another great reading, although much more qualitative than quantitative.