Answers in this area are in the grey area and should be handled on a case to case basis.
In any case, if you think the answer is not a serious one or is plain wrong, feel free to downvote it. This shows both the user and the community that answers like it are not preferable. The user may even remove it them self at that point.
As for flagging it as low quality, this should only be done in cases where it is more joke that informative (i.e. not posted in good faith). Sometimes silly sounding answers are legitimate, though perhaps not the best solution or a favorable one. To know the difference, some research will have to be done. Hopefully the answer is a good one and thus provide the research in the answer itself, but more often than not they won't. If they don't, that's more reason why you could choose to downvote.