There’s more of an Inyun to eat Yoshon then Cholov Yisroel.
What’s wrong with Cholov Stam? Can we trust the Goyim? Obviously if Rav Moshe even thought that there was a doubt then he wouldn’t have said it was ok. He was machmir, just like if a Rav says that you could hold by an Eiruv and he doesn’t.