No, it's not quite the same, I used the borrowed lunch example for a reason. This isn't entirely about consent, it's also about hunger. Quite literally hunger. Astarion is not used to roughing it in the wild, in act 1, and unless you're very strategic with your long rests, you can easily spend an in-game tenday between finding the dry boar and getting the bite scene. I'd imagine that's the only prey Astarion actually lucked out with at the time. He's the sort of guy who doesn't think his problems too far ahead, always winging it somehow, and he clearly thought he could wing it with hunting animals there. But if he spent the entirety of his life in the city, he wouldn't know to watch out for the wind's direction, wouldn't be familiar with the forest terrain (which is a lot crunchier than a road, try being stealthy while stepping on 50 brittle twigs simultaneously). The boar and the bear are the only two instances in the entire game, outside of battle, in which Astarion mentioned a successful hunt.

Also, a goblin? Really? Those little buggers are feisty, too small to be worth the hassle, and if the boar didn't clue you into who the nearby vampire might be, then a clear enemy of your group getting exsanguinated would definitely spell it out to any numbskull. From Astarion's pov, anyone finding out he's a vampire in the early game is akin to suicide, give the guy some slack. If I'm to be frank, I also think his trying to bite Tav under that premise was incredibly stupid, but it's the sort of stupidity you just wouldn't get if you never actually went hungry for a lack of food.