They probably made a product with that slug by accident and are doing that to try to get it removed from search engine results.

It makes me wonder if Nordstrom ever stocked the now-defunct Pornstar clothing brand.

Disallow is used to exclude certain URLs from being crawled, in this case it looks like a search query as the store's search uses this pattern: http://shop.nordstrom.com/sr/query .

Maybe some mal-intended inbound links that they don't want to be associated with?

Is this some sort of new terrible negative seo? Associate a target url for a bunch of negative things?

Maybe that was their intention, but that's not how it's done.