http://new.spring.me/#!/JESawyer/q/455236873976046877 is what you're referring to, which MAY be the case, but it's unclear. There he's referring specifically to "unused dialog in the GECK" which might be even more convo topics that were never actually voiced, not neccesarily this and the lines for Cook-Cook and Violet. I say this because Sawyer specifically addresses Nephi discussing being Mormon, which simply doesn't exist within those vids. Could be the Mormon dialog was cut and then again the basic dialog was left out.
Looking into it now though and trying to figure out what the story is.
EDIT: http://fallout.gamepedia.com/Driver_Nephi%27s_dialogue There's even more cut dialog that I'm guessing never got audio files. I don't think it's present in cut content mods either.