It's not aggression, it's feeding mode pure and simple. It's why you shouldn't be handling a snake around feeding time. Feed in the cage. Bites from a bp feel like absolutely nothing though, it's good you know that now because it can be helpful to not fear them later. It's more the surprise/startle than anything else. I've been tagged by a couple being stupid with my hand in the cage removing uneaten rats or ignoring clear signs of feeding mode and it feels like teeny pinpricks. You learn what not to do next time and that's best on a snake that can't hurt you.