But the packaging itself matters, eg soda in a Al can and a glass bottle is perceived quite differently.
If the milk came in a plastic bottle I have no problem drinking directly from the bottle, if it came in TetraPak... If I bothered to cut it with scissors I would probably be fine drinking milk directly, but if I just ripped the corner by the perforation then I would definitely drink from the mug, because I hate the feeling of the paper fibers on my lips.
Also there is a thing with Americans, they just buy milk. I can't buy "just" milk. I can buy 1%, 1.5%, 3.5% and (my preferred) ~3.5-4% fat milk. I don't like 1%, it is just a water with a bit of milk taste for me. Even reading Wikipedia article on skimmed milk makes me wonder how it even can be called a milk. I read many stories of Americans who didn't like milk since their childhood, only to discover in their adult life what what they drunk back then wasn't even a milk per se and sometimes their parents not only gave them skimmed milk but further diluted it with water. Urgh!