Just to clarify what mdg said,
Legally cassein, whey, lactose etc are not milk.
The phrase “may contain …” is not fda regulTed. So if a product doesn’t contain milk but does contain lactose it is halacikly milchig yet legally not.
This is especially problematic with lactose and it’s derivatives since allergy to milk is usually to proteins.
Bottom line is to call the hashgacha and find out. The fda and legavdil halacha have different rules/regulations and definitions