dyw and dydy are identical in meaning in this context.
They are simply alternative forms both derived from the more formal form (not used on this course) nid ydyw. The d- is the end of nid (a negative marker) and the -ydy or -yw is simply taken from one end or the other of ydyw.
He wouldn't want milk as he is an owl, and avians lack the enzymes needed to break down lactose. Can you imagine birdmilk?
No, no, um... cow farts are polluting the world and he does not like that