I didn't downvote, but I considered voting to close your question as "unclear what you're asking".
The tooltip for the downvote button says "this question does not show any research effort; it is unclear or not useful".
- It must be quite easy to find at least some information on how many editions of Watership Down there have been. I put "watership down editions" into Google and immediately came across this list, which doesn't answer your question but is at least a start. Including some basic research like this in your question would have improved it.
- Your question is also kind of unclear, since you don't say where you found this review or go into much detail about what it said, so it's very hard to tell what the evidence is that there might be different versions of the book.
- Finally, "not useful" is more subjective, but someone might have downvoted it because they saw it as a trivial question and didn't care about the answer.
(Again, I didn't downvote, so all of this is just speculation on why people might have done so.)
I was vacillating about whether or not to vote to close your question. As mentioned above, it's quite unclear; without more details about the review, it's hard to see what the motivation is for your question. If there are different versions of the book, we'd have no way of saying which of them was likely to have inspired that review, which makes the question hard to answer.
My strong suspicion that there aren't different versions - that all the various editions of the book differ only in cover and packaging, and not in the essential text of the novel - is the main thing that stopped me from voting to close. If this suspicion is correct, then your question is answerable.
I hope this helps! I wrote it up pretty quickly, but hopefully it might help you to understand why people had issues with your question.