>1. Перелейте молоко/молока из бутылки в кастрюлю.
> 1. молоко is the only option.
Pour the milk from the bottle into the pan.
Then how about
Pour some milk from the bottle into the pan. ?

Can you follow the rule: for "some X" use genitive. ? This would be like the Partitive Genitive.

This would seem to be why it is correct to use both in the sentences. With no context, either is possible.