It actually does contain it in the ingredient list (I.e. sweet cream). It just that the FDA requires an additional label warning of allergens, like contains nuts or milk, which is what this was missing.

Any reason you conveniently left out the start of the sentence you’ve quoted? Because the bit you’ve left out changes the tone pretty significantly.

In this particular situation I’d deem positive confirmation to be something like a vegan certification, as opposed to the absence of something.

Combine the absence of milk from the ingredients on something advertising itself as butter with no other distinguishing information and that adds up to suspicion for me.

That's not a positive confirmation.