this understanding of metaphors is not that it was used then. the understanding happens today a contemporary application of historical knowledge.
and honestly, it's obvious.
https://www.splcenter.org/resources/reports/lying-about-ausc...
edit: ...also I didn't know it was even used this way, back then, see my TIL reply in some "cousin" comment.
If it was a well accepted term it’d be one thing, but when made up on the spot it very much sounds like “place we sen out undesirables” to me.