Having now read further in Guyau it appears that he interprets Epicurus one way, but understands Epicureanism another way. His thoughts on Epicurus don't always agree with ours, but his thoughts on using the philosophy seem to.
Part of his approach is that philosophies, like organisms, grow and evolve. So in reading the book it's possible to take issue with some of his interpretations and still get a lot of benefit from his presentation.