I'll bet it was.
I don't think mothers should seduce there sons in real life, you understand, I just find the power dynamic hot were it's the boy who's all "I-I don't know... " and a more powerful, more experienced woman is taking control.
In the context of hentai, if the writer is good enough, any number of horrible things can be made to seem sympathetic or right for the characters but that doesn't mean that it ever actually happens like that in real life.
Yeah, though in this he didn't know it was his mother (well, sort of), it was explicitly an Oedipus Rex situation.
For the literarily inclined, it's "Kafka on the Shore" by Haruki Murakami, a writer whom I would recommend to anyone.
Speaking of unbelievably confessed hentai interests, I've always had a thing for older sister-younger brother incest. (well, not strictly that age dynamic, just no "older brother getting pedo for his 12-year-old sister types".