Recently I've been finding this product in a supermarket. Does this mean 70/30 protein/fat? I tried to look this up online, no success.
"Does this mean 70/30 protein/fat?"
It's likely that they are rewording the protein/fat ratio since 70/30 is pretty shitty ground meat, especially if it's CAFO meat, where you'd want to avoid CAFO animal fat if possible to maintain a better Omega-3:6 ratio.
If you cook, I find 85/15 to 90/10 ideal for most general uses. Still, try to avoid the CAFO stuff if you can.
Yes it's fat percentage by weight, and although there are trace carbs from glycogen in meat, the other 70% by weight is protein. BUT ... that protein part is high water content. So 100g of <30% fat contains roughly 30g fat, 70g lean but not 70g protein.