I generally view edits to answers a bit differently than edits to questions as I have seen some issues with people making radical edits to answers, thinking they were doing the right thing, but they ended up making a mistake (and with the current state of the approval processing, the edits were accepted).
I would normally reject an edit that changes an answer unless:
- I am 100% certain the edit is valid and correct
- The editor left a comment for the answerer stating the necessary changes
- The original answerer did not object via comment
The problem is two-fold. First, answerers tend to be more protective about the content of the answers as their name is attached to it, so they don't want someone making a change that would reflect negatively on them. Second, it can be tough to get a fix approved because of common practice that discourages edits that change answers.
I do agree that the answer doesn't belong to the answerer anymore, nor does it belong to the OP. It belongs to the community as a whole, so the community should be able to edit it as needed. However, the original poster (of the answer) should be given the right of first refusal to make the suggested changes or at least explain why he/she objected to it.
I saw a case once where someone suggested an edit that added a substantial content to an answer (even more so than what was suggested in this case), and that edit was accepted. But it turned out that the edit was wrong, and when the original suggester realized his mistake, the suggested edit to fix it was rejected, so you were left with an incorrect accepted answer.
In this specific case, I think the edit should have been rejected. If the question OP has something else to add, a comment would have been appropriate, and maybe even another answer (I'm not familiar enough with the content of this answer to make a decision on that).