I presume that this is what happened because a) she has a paperback & eBook edition of this book, b) this happens a lot, and c) someone complained. I would hope that Amazon would do a search in the eBook and not only look at the total hyphens, but also find a few examples of words that were probably broken up for print layout reasons. If so the author should remove the hyphens and resubmit the eBook.
If that's not the case, it's very silly. Obviously hyphens are useful and shouldn't be banned.
That would have side-effects e.g. https://en.wikipedia.org/wiki/Double-barrelled_name
Or have to quote transliterated Arabic, for that matter.
[edit: It appears, though, that the author is stylistically abusing hyphens, so while they may not be wrong, they're grating to most readers. So, should Amazon be in the business of banning books on the grounds of poor style, rather than technical grounds that are inarguable? (If the book contained the word hyphen-ated, that would be wrong unless it was dialogue and the speaker was pausing between syllables.)]
Graeme merely asserts that his book was free of those, which we knew going in. It does nothing to say why Amazon was raising the issue, and it wouldn't shock me that an automated system would be unable to tell the difference.
Btw, the author's name appears to be "Graeme", which seems to always be male: