“Meat shield” is not a new term and explicitly means using another human to prevent being shot / killed. That’s all people are saying about Musk’s behavior when they refer to him using his kid in this fashion. Nothing beyond that (by that specific term anyway).

https://en.m.wiktionary.org/wiki/meat_shield

https://en.m.wiktionary.org/wiki/human_shield#English

That doesn’t change the fact his father is using him as an anti-assassination accessory. It’s in no way criticizing the kid, but calling out his father’s abhorrent behavior. In fact we should call it out because maybe it will shame Musk into stopping (of course it won’t).