I'm fine with the undelete, but only because the page actually says that it is public domain and therefore very unambiguously not copyrightable. Almost any other content license could pose concerns, since it might be incompatible with our own CC-wiki. The notable exception is Wikipedia which has the same license.
Since we're on the subject, I want to point out a few things in the broader context:
If an entire answer is just regurgitated copypasta, it adds no value whatsoever to our site because the same information (literally) could be found with a Google search. Summarizing, consolidating, or elaborating on information from other sources has intrinsic value; copying it does not. We should downvote and/or delete these answers not simply because of any legal risk but also (maybe primarily) because it doesn't improve the internet to have two search results where one is exclusively quoted material from the other.
Allowing these types of answers to be upvoted, unless relegated to unusual or extreme situations, opens the door to rep farming. In this case the source was reliable (the USDA) but the same user has also (re)posted several answers lifted from eHow, wikiHow, etc. If we know that an answer was plagiarized and do nothing about it, then we undermine the system that's designed to make Stack Exchange sites reasonably trustworthy. This would not be the first time in Seasoned Advice's history where we've been forced to delete plagiarized answers simply because they were being mindlessly upvoted.
Sometimes it's better for a question to have no answers than to have one or several poor answers with upvotes. That is because the former category appear in the unanswered questions list and are more frequent candidates for bounties and other incentives. Moreover, a highly-upvoted answer, even if it is not original, can discourage others from contributing answers that are original and potentially just as good/relevant. It's not just a matter of "punishing" plagiarists, we also want to encourage others to write their own answers and improve the site.
A citation is not an excuse to present someone else's content as your own. I am not a lawyer, but the issue has been discussed several times on several sites, and the general consensus is that (a) the material must be quoted, not merely presented above/below/around a citation, and (b) the quoted portion should be no more than a few sentences long; several paragraphs is generally not acceptable. This still doesn't guarantee that it's OK, but at least it's semi-defensible as fair use.
Bottom line, we are not lawyers and do not need or want the risk of a copyright dispute, nor do we want to reward or continue to collect lazy, thoughtless word vomit ripped off from other sites on the internet. Not that we should start a witch hunt, obviously, but we should be just as aggressive about removing content duplicated from other sites as we are about removing content duplicated from our own site. Otherwise we will quickly lose all credibility with the expert audience that we're trying to attract.