It could be both, too...

Oh, and following indefatigable42's advice to put "Walla, walla" in the search term string worked, and I learned that Father was telling me the truth, in part -- "peas and carrots" is one thing (of several options) that background actors can say for word noise.

I think it only became a catchphrase for mindless talk just for the two of us, though -- a private joke...