He didn’t say why. He said it in response to my bringing up the Nirbater Rov’s opiniin, so that is the implication.
The DA issue came to the forefront after Rav Moshe was niftar, and I don’t think (but could be mistaken) that he was quoted as being mattir.
Rav Dovid does apparently still hold that cholov stam is muttar mei’ikar hadin, so that would mean that he is meikil on both issues. My point is just that the heter applying today is not l’kulei alma, but there’s still whom to rely upon.