It’s a machine learning chat bot, not a calculator, and especially not “AI.”
Its primary focus is trying to look like something a human might say. It isn’t trying to actually learn maths at all. This is like complaining that your satnav has no grasp of the cinematic impact of Alfred Hitchcock.
It doesn’t need to understand the question, or give an accurate answer, it just needs to say a sentence that sounds like a human might say it.
Unless you’re a raw milk TB-chaser type the milk you drink is probably processed too. Being processed doesn’t make something inherently worse, and “no nutritional value” is a daft claim. OK if you consume milk as your only source of protein or fat, you probably want to choose your milk substitute tailored to whichever the rest of your diet is deficient in, but better or worse for us is a fairly arbitrary concept.
Livestock for dairy production are unarguably bad for the planet though.