It's hard to describe exactly, so first look at the releases for Twilight Princess. The game was released on GameCube and Wii, but only the Wii version has widescreen support. The releases have been updated to reflected this.
Now let's say I'm looking for GameCube games with widescreen. I set the filters on the form accordingly, and when I submit the form this is what I see. Both GameCube and widescreen are required for my search, and Twilight Princess is included in the results because it is available on GameCube and also has releases with widescreen support. There is no release of Twilight Princess that actually fits both requirements I've set, so it shouldn't show up in the search results.