I mean, this risks just arguing over semantics, but I wouldn't call any part of the gameplay itself a bonus. You can't remove the card draw without changing the strategies available to a druid player, unlike things like the game's presentation. When I think of a Hearthstone easter egg, I think of playing Snowflipper during the Lich King fight.
Now, if you want to say that such interactions are things Blizzard wants to be discovered, same as the other undocumented cards like spare parts or toxins, then I'd agree. But I'd also say the game shouldn't be pushing you to online resources, just to find out everything a card can do. At that point, you're not even looking at interactions or strategies or the advanced rulebook yet.