In UploadWizard's Flickr importing interface, if you enter the URL of a single image such as https://www.flickr.com/photos/winnu/50811285123/, it sets the author as the Flickr realname (in this case "Nigel"). If, however, you enter the URL of a photostream such as https://www.flickr.com/photos/winnu/with/15715931764/, it sets the author as the Flickr username (in this case "winnu").

In both cases, it should set the author to the realname if possible (photo->owner->realname).