Rav Moshe did not use the term “Chalav Stam” – regular milk;
He used the term “Chalav Companies” – milk from companies. He transliterated “companies” from English to Hebrew. I’m not sure when/how we got the term “Chalav Stam”
IMHO, Rav Moshe was matir “chalav companies” because of the policies and procedures that we have in place in the USA. But if you were to buy milk in a different country or buy directly from a farmer who normally does not sell milk, you can’t assume the same level of kashrut.