You could take your Hit Actor and Cast To Landscape - if successful, it’s a landscape.
Or take your Hit Component and Cast To LandscapeComponent - if successful, you’ve hit a landscape.
Or you can use GetClass on the Hit Actor and see if it equals Landscape.
Or GetClass on the Hit Component and see if it equals LandscapeComponent.
Or you could apply custom physical material to your landscape, and then check if the HitResult::PhysMat matches.