Why du lait and not le lait?
The question is do you drink milk in general not did you drink some milk.
I could guess this could be a time when du lait would be are you drinking some milk where le lait would be do you drink milk. That's some context.
It might be a bit of lag when you you click play, it sounds pretty clear to me. Most French I hear sort or pronounce "tu" with a bit of a "ch" tossed in. Almost like an Irishman counting to three. "One, tchoo, tchree"