voyeur-only friend wants to join — what category is even that

so we have a friend (single guy, 40s, weve known him 5+ yrs) who has slowly come out as being into the lifestyle. he doesnt want to participate AT ALL, he just wants to watch and maybe touch himself. my wife is actually really into the idea, im weirdly more hesitant. but more importantly what do u even call that. its not soft swap (he's alone). its not full (he isnt touching anyone). its not unicorn-anything. is this just voyeurism and we're overthinking the category? has anyone done a "watcher only" arrangement and how did u set up the boundaries