Think of the 'little miss muffit' ....eating her curds and Whey.
Curds and whey together are like cottage cheese. The lumps are Curds
(Cheese, Casein), and the whey is Liquid=likely Lactose, or think of
it as Whey=Water.

So there's a small amount of lactose in the casein part (otherwise it
would be hard). But there's much more chance of lactose in the whey,
unless the manufacturer chose to purify it.