It must be doing some kind of personalization for you, because when I load those two links in an incognito window, the first page is made up entirely of links to the constrained domains. That differs from the parent's link which in an incognito window just displays some kind of bing-looking error message
https://www.bing.com/search?q=site%3Aredhat.com
https://www.bing.com/search?q=site%3Asuse.com