Two of the predefined flags, which you can raise against an answer, are as follows:
What do they mean, when should users use them, and how or when should moderators react to them?
So far as I can gather:
"Not an answer" is when something should have been posted as a new question, or posted as a comment, instead of as an answer.
"Very low quality" is when the post is too short to be an answer; or isn't written in English; or isn't about Buddhism; or something like that.
Neither of these flags should be used for a "wrong" answer, nor for an answer which is only partially relevant to the question.
If it's trying to be an answer, if it's written in English, if it's about Buddhism, if it isn't rude or hostile, then it probably shouldn't be flagged at all. If you think it's a "wrong" answer, or just not a helpful answer, then downvote instead of flagging it.
Moderators normally won't delete a valid answer -- so long as it confirms to various rules, like not being hostile and like being about Buddhism -- unless several users downvoted it.