Of course they should appear as videos because they are VoDs and are accessible even while the stream is still live. They just don’t have a thumbnail generated until the broadcast has finished, which you can experience on Twitch itself by going to the VoDs page of a channel that’s live and you’ll see that the VoD of the currently live stream lacks a thumbnail and just has the generic image for when a video lacks a thumbnail.
Also, v5 does return these videos in API requests, so the API is consistent in what results it is showing.