That doesn't seem like a very good example of extreme hyphenation, at least to me. I only count 4 on the entire page.
One thing I do notice about it is that it is blocked left and right - i.e. each line is spread out over the entire area with an even right margin. On epub files you yourself have control over, you may be able to specify how that operates somewhere in the epub file (probably in the .css style file). I think it is hard to decide which kind of blocking causes more hyphenation.