I declined this "rude or abusive" flag.
The relevant guidance on main meta for when to use the rude/abusive flag is:
If an otherwise valid post contains vulgar words as an expression of frustration, edit the bad part out instead of flagging the entire post as rude or abusive. If this results in an edit war or you expect this to happen, flag for moderator attention instead.
The post has a positive score at this time so it certainly seems to me to be an "otherwise valid" post (I am not familiar with the topic so I can only judge by the voting). It also doesn't contain "vulgar words as an expression of frustation" (just a "sigh", which may not even be directed at you). Personally, I don't think it's contemptuous but others may disagree.
The best course of action seems to be to edit out the parts that you think are insulting (if the answerer reverts such an edit feel free to flag for a moderator's attention). If I had marked that flag helpful the post would have been deleted and the answerer would have been penalized 100 reputation. I think that answer has valuable information which should not be deleted, and I don't think the answerer deserves a 100 reputation penalty over a "sigh".